Add support for both WinUI 2 and 3 under Uno platform

[Arlodotexe]

This PR introduces the ability to switch cross platform Uno heads and libraries between using WinUI 2 and 3.

• Closes Full support for Uno Platform #28
• Add UseUnoWinUI.ps1 - a PowerShell script to switch cross platform Uno heads and libs between Uno.UI and Uno.WinUI.
• Cleans up - Remnants of previous attempts at this that used MSBuild
• Consolidates Uno packages - Under a single Labs.Uno.props file.
• Heavily tested
  • Both in Visual Studio and from the CLI with MSBuild
  • Each head under both WinUI 2 and 3
  • With the minimal required TFMs and with All TFMs
  • Single-sample solution and All solution

[Arlodotexe]

@michael-hawker We should resync on what we want the Build Validation pipelines to look like with these changes.

• Building under both WinUI 2 and 3 for Uno as part of the All solution build validation?
• Possibly splitting WinUI 2 / 3 into their own build pipelines for faster and cleaner validation when something is wrong?

[michael-hawker]

@Arlodotexe had put a break down in the issue here: #28 (comment)

Let's add another job to the pipeline so that in one it'll build and validate on WinUI 2 and create the WinUI 2 based packages, and then in the other it'll do the WinUI 3.

We'll need the Uno switch script to when in WinUI 2 mode to change the NuGet Package Identifier in the Experiments csproj to be .Uwp. vs. .WinUI.. If we don't change the file/assembly name, but just do it as the package identifier we shouldn't have to mess with anything else, right?

[Arlodotexe]

Let's add another job to the pipeline so that in one it'll build and validate on WinUI 2 and create the WinUI 2 based packages, and then in the other it'll do the WinUI 3.

So we'd effectively just copy the existing pipeline, but add in the WinUI 3 switch for Uno?

We'll need the Uno switch script to when in WinUI 2 mode to change the NuGet Package Identifier in the Experiments csproj to be .Uwp. vs. .WinUI.

I'll do some tinkering and see about importing that part of the PackageId as part of the Uno props file.

[Arlodotexe]

Implemented and tested outputting different packages with different PackageId for WinUI 2 / 3

[michael-hawker]

Looking good. How does this work for the UWP/WinAppSDK heads in the Experiment projects? Do they just still work by default?

[Arlodotexe]

Looking good. How does this work for the UWP/WinAppSDK heads in the Experiment projects? Do they just still work by default?

Yep, this is just for Uno. Both WinAppSDK and UWP should continue to work whether Uno is using WinUI 2 or 3, both in the IDE and in the nupkg since they're under different TargetFrameworks.

[michael-hawker]

Everything passed in the Action, so not sure why it's stuck...?

Maybe we'll see on another pass later with the next change?

Like the individual commit is showing green:

[michael-hawker]

Ah, yes, it's waiting on the status of the pipeline called build because of this setting:

We'll have to update this.

[michael-hawker]

Couldn't get the experiment to run the WASM head in WinUI 3 mode, just was blank page after Uno logo. Worked fine in default WinUI 2 mode though (as did the UWP/WinAppSDK heads).

[michael-hawker]

ah, just tried to change branches and got this:

Would that be the difference with the other flag you mentioned @Arlodotexe?

Doing a git reset --hard did change that file back in the present form though, and then let me switch branches.

[michael-hawker]

Is the PowerShell guidelines for naming convention be uppercase for like AllowGitChanges so the flag is -AllowGitChanges on the commandline?

[michael-hawker]

@Arlodotexe mind turning the verbose on the uno check so we can get more details?

Edit: nvm, realized I could do it. Just wanted more info as it looked green.

[michael-hawker]

Confirmed this is a transient issue due to a Google url with Uno Check.

[michael-hawker]

Arlo confirmed that the WASM WinUI things work in a separate app, so we'll commit this and then fix forward with tracking issue #77 as we default to the working WinUI 2 versions for now.