Add support for analyzers from ref-packs

[ericstj]

Also add analyzers to conflict resolution.

Implements https://github.com/dotnet/designs/blob/main/accepted/2021/InboxSourceGenerators.md

[ghost]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[ericstj]

@dsplaisted @wli3 can one of you have a look at this and give some guidance around what might be missing? I did what I think might be the minimum to enable the scenario but I expect to need to do more :)

[dsplaisted]

Looks good. Is there any way to have test coverage of analyzer conflict resolution?

[ericstj]

Did you have a suggestion for where to look for such tests, @dsplaisted? I saw tests of the conflict resolver itself, but nothing that tested the task level where this logic lives. I might be missing something though.

[ericstj]

Perhaps here: https://github.com/dotnet/sdk/blob/main/src/Tests/Microsoft.NET.Build.Tests/GivenThatWeWantToResolveConflicts.cs?

[safern]

Looks good.

[ericstj]

I added a test that forced inbox and OOB SDK analyzers to be used. I made it fail locally by disabling the conflict-resolution change in targets:

C:\src\dotnet\sdk\artifacts\bin\redist\Debug\dotnet\sdk\6.0.100-dev\Sdks\Microsoft.NET.Sdk\analyzers\build\Microsoft.CodeAnalysis.NetAnalyzers.targets(580,5): warning : The .NET SDK has newer analyzers with version '6.0.0' than what version '5.0.3' of 'Microsoft.CodeAnalysis.NetAnalyzers' package provides. Update or remove this package reference. [C:\src\dotnet\sdk\artifacts\tmp\Debug\AnalyzersAreC---4DE360D4\AnalyzersAreConflictResolved\AnalyzersAreConflictResolved.csproj]
CSC : error CS8034: Unable to load Analyzer assembly C:\src\dotnet\sdk\artifacts\.nuget\packages\microsoft.codeanalysis.netanalyzers\5.0.3\analyzers\dotnet\cs\Microsoft.CodeAnalysis.CSharp.NetAnalyzers.dll : Assembly with same name is already loaded [C:\src\dotnet\sdk\artifacts\tmp\Debug\AnalyzersAreC---4DE360D4\AnalyzersAreConflictResolved\AnalyzersAreConflictResolved.csproj]
CSC : error CS8034: Unable to load Analyzer assembly C:\src\dotnet\sdk\artifacts\.nuget\packages\microsoft.codeanalysis.netanalyzers\5.0.3\analyzers\dotnet\cs\Microsoft.CodeAnalysis.NetAnalyzers.dll : Assembly with same name is already loaded [C:\src\dotnet\sdk\artifacts\tmp\Debug\AnalyzersAreC---4DE360D4\AnalyzersAreConflictResolved\AnalyzersAreConflictResolved.csproj]

Then put my change back in place and it succeeds.

I think this is ready to go.

[ericstj]

Tested this with the work I have in PR in arcade/runtime and it's working as expected. Thanks folks!