Add net8.0-windows to WinAppSdk

[Arlodotexe]

This PR adds net8.0-windows10.0.22621.0 as a supported TargetFramework on all WinAppSdk components.

Closes #164

[Arlodotexe]

Still blocked on the issue detailed here, but msbuild extras has been fully removed from all targets except UWP, and all resulting errors have been fixed.

A few (new?) warnings that need resolved, either here or in a separate PR:

Release tracking and diagnostic descriptor formatting:

        D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\CommunityToolkit.Tooling.SampleGen\Diagnostics\DiagnosticDescriptors.cs(216,9): warning RS2008: Enable analyzer release tracking for the analyzer project containing rule 'TKSMPL0015' (https://github.com/dotnet/roslyn-analyzers/blob/main/src/Microsoft.CodeAnalysis.Analyzers/ReleaseTrackingAnalyzers.Help.md) [D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\CommunityToolkit.Tooling.SampleGen\CommunityToolkit.Tooling.SampleGen.csproj]
    D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\CommunityToolkit.Tooling.SampleGen\Diagnostics\DiagnosticDescriptors.cs(201,9): warning RS2008: Enable analyzer release tracking for the analyzer project containing rule 'TKSMPL0014' (https://github.com/dotnet/roslyn-analyzers/blob/main/src/Microsoft.CodeAnalysis.Analyzers/ReleaseTrackingAnalyzers.Help.md) [D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\CommunityToolkit.Tooling.SampleGen\CommunityToolkit.Tooling.SampleGen.csproj]

A warning about an EnforceExtendedAnalyzerRules property that needs to be enabled for our source generators:

        D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\CommunityToolkit.Tooling.SampleGen\ToolkitSampleMetadataGenerator.Documentation.cs(17,22): warning RS1036: 'CommunityToolkit.Tooling.SampleGen.ToolkitSampleMetadataGenerator': A project containing analyzers or source generators should specify the property '<EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>' [D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\CommunityToolkit.Tooling.SampleGen\CommunityToolkit.Tooling.SampleGen.csproj]

A few conflicts with System.Collections.Immutable on the test heads that need resolved:

      "D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\ProjectTemplate\ProjectTemplate.sln" (default target) (1:2) ->
  "D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\ProjectTemplate\heads\Tests.WinAppSdk\ProjectTemplate.Tests.WinAppSdk.csproj" (default target) (6:6) ->
  (ResolveAssemblyReferences target) -> 
    C:\Program Files\Microsoft Visual Studio\2022\Enterprise\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(2382,5): warning MSB3277: Found conflicts between different versions of "System.Collections.Immutable" that could not be resolved. [D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\ProjectTemplate\heads\Tests.WinAppSdk\ProjectTemplate.Tests.WinAppSdk.csproj]
  C:\Program Files\Microsoft Visual Studio\2022\Enterprise\MSBuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(2382,5): warning MSB3277: There was a conflict between "System.Collections.Immutable, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" and "System.Collections.Immutable, Version=7.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a". [D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\ProjectTemplate\heads\Tests.WinAppSdk\ProjectTemplate.Tests.WinAppSdk.csproj]

Wasm head might need an explicit reference to the latest Microsoft.CodeAnalysis packages:

     "D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\ProjectTemplate\heads\Wasm\ProjectTemplate.Wasm.csproj" (default target) (8:6) ->
    (CoreCompile target) -> 
      CSC : warning CS9057: The analyzer assembly 'C:\Program Files\dotnet\sdk\8.0.201\Sdks\Microsoft.NET.Sdk.Razor\source-generators\Microsoft.CodeAnalysis.Razor.Compiler.SourceGenerators.dll' references version '4.9.0.0' of the compiler, which is newer than the currently running version '4.8.0.0'. [D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\ProjectTemplate\heads\Wasm\ProjectTemplate.Wasm.csproj]
      D:\a\Tooling-Windows-Submodule\Tooling-Windows-Submodule\tooling\ProjectTemplate\heads\Wasm\Uno.UI.SourceGenerato

[Arlodotexe]

Looks like our blocker was resolved by this commit, but some lingering issues still remain regarding package conflicts and new analyzer warnings (see here).

[Arlodotexe]

Looks like something broke when EnforceExtendedAnalyzerRules was enabled on the source generators. Tests aren't able to see emitted Diagnostics for some reason, looking into it. More info here: dotnet/roslyn-analyzers#6115