Values in CompilerVisibleProperty containing #s don't transfer to source generators

[MichaelSimons]

Razor's source generator adds the RootNamespace MSBuild property to the list of CompilerVisibleProperty. It uses this to calculate namespace for the generated types. In the GeneratedMSBuildEditorConfig.editorconfig, the value that gets written to is build_property.RootNamespace = C#_blazorwasm. The value that the source generator reads it is C which results in a bunch of code generation errors.

For some file metadata read by the source generator, our SDK currently does some custom encoding to avoid this issue. I'd like to avoid doing this for this metadata because the issue isn't unique to Razor and other SG authors are also likely to get in to trouble because of it.

---

Original issue description:

Steps to Reproduce

1. Using .NET sdk 6.0.100-rc.2.21471.7
2. mkdir C#_blazorwasm
3. cd C#_blazorwasm
4. dotnet new blazorwasm
5. dotnet build

Actual Results
Project fails to build

Microsoft (R) Build Engine version 17.0.0-preview-21378-03+d592862ed for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
d:\test\blazor\C#_blazorwasm\Pages\Index.razor(7,1): warning RZ10012: Found markup element with unexpected name 'SurveyPrompt'. If this is intended to be a component, add a @using directive for its namespace. [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
D:\test\blazor\C#_blazorwasm\Program.cs(2,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]

Build FAILED.

d:\test\blazor\C#_blazorwasm\Pages\Index.razor(7,1): warning RZ10012: Found markup element with unexpected name 'SurveyPrompt'. If this is intended to be a component, add a @using directive for its namespace. [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
D:\test\blazor\C#_blazorwasm\Program.cs(2,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(9,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
d:\test\blazor\C#_blazorwasm\_Imports.razor(10,7): error CS0246: The type or namespace name 'C__blazorwasm' could not be found (are you missing a using directive or an assembly reference?) [D:\test\blazor\C#_blazorwasm\C#_blazorwasm.csproj]
    1 Warning(s)
    17 Error(s)

Excepted Results
Project builds cleanly with no errors.

[pranavkm]

Possibly related issue: #44596

[sharwell]

Duplicate of #51692