Client library for querying .NET platform dependency files

[mthalman]

This defines a client library project (dotnet/core#5647), to be published as a package, that can consume the platform dependency schema. The proposed model that implements this schema is available at dotnet/core#6170.

The library provides an API to load and validate the model and access all its state.

It also provides higher-level APIs rather than only exposing the raw state of the model. Specifically, it provides a parsed expression representation for dependency names and resolving of dependencies within a platform hierarchy.

[mthalman]

cc @MichaelSimons, @NikolaMilosavljevic, @dleeapho, @rbhanda

[mthalman]

The build failures are unrelated to my changes. The same errors occur in main branch. I've logged #115.

[NikolaMilosavljevic]

Build infra changes look good. I have not reviewed the library code.

[MichaelSimons]

Excuse my lack of Arcade knowledge. What is this section for and why is TargetsWindows the only property set if this is a cross plat library?

[mthalman]

I had just copied this from Microsoft.Deployment.DotNet.Releases. I see that clickonce defines things differently. @NikolaMilosavljevic - Where did you get the content for that file and why are the Targets* properties defined differently than it is for Microsoft.Deployment.DotNet.Releases?

[MichaelSimons]

@NikolaMilosavljevic - is all of this necessary?

[MichaelSimons]

@mthalman - Is this PR still relevant?

[mthalman]

@mthalman - Is this PR still relevant?

😬 No. There's more work needed in the overall design. I'll close this.