Consolidate Razor compiler code into a single DLL

[jjonescz]

Merge the following DLLs into one (Microsoft.CodeAnalysis.Razor.Compiler):

• Microsoft.AspNetCore.Razor.Language (move into folder Language)
• Microsoft.CodeAnalysis.Razor (move into folder CSharp)
• Microsoft.NET.Sdk.Razor.SourceGenerators (move into folder SourceGenerators)
• Microsoft.AspNetCore.Mvc.Razor.Extensions (move into folder Mvc)

Merge tests into one project, as well (Microsoft.CodeAnalysis.Razor.Compiler.Tests).

Roadmap:

• Transport Microsoft.AspNetCore.Mvc.Razor.Extensions v1 and v2 into SDK and make rzc.dll tool use them.
  • Transport v1 and v2 of MVC extensions #9266
  • Use MVC extensions from Razor transport sdk#35273
  • [8.0.1xx] Use MVC extensions from Razor transport sdk#35371
• Rename compiler assemblies #9129 to see whether anything breaks
  • Use Razor with renamed compiler DLLs sdk#34928
  • [release/8.0.2xx] Update dependencies from dotnet/razor sdk#36059
  • [main] Update dependencies from dotnet/razor sdk#36041
  • Use SDK with renamed Razor compiler DLLs aspnetcore#50369
  • in Roslyn: Rename Razor compiler assemblies roslyn#69655
    • Add IVT to a future unified razor test project roslyn#70485
    • No longer needed as we removed the IVTs: Removing Microsoft.CodeAnalysis.ExternalAccess.RazorCompiler roslyn#71024
      • When IVTs are fixed in Roslyn, re-enable host outputs in Razor. Re-enable host outputs #9447
      • Clean this up after merging of DLLs into one is complete.
• Fixup runtime compilation which lives in aspnetcore. Runtime compilation is fixed to v6.0 of Razor.
• Fixup roslyn, aspnetcore, and sdk repos when the update flows there (and again when the updated aspnetcore flows back into sdk), for example:
  • https://github.com/dotnet/roslyn/blob/3630eb1758c131d0f359704a0e8cc874e109d269/src/VisualStudio/Core/Test/ProjectSystemShim/VisualStudioProjectTests/AnalyzerReferenceTests.vb#L212
  • https://github.com/dotnet/aspnetcore/blob/0684c8aa38c6b9926bae3d901741a83c453dc413/eng/Dependencies.props#L16
  • https://github.com/dotnet/sdk/blob/cfa6ec2353784e22171bc4539181a1a935e066e9/src/Tests/Microsoft.NET.Sdk.Razor.Tests/ScopedCssIntegrationTests.cs#L93
• Redo Move compiler code into the new project #8471 and when complete, redo the steps above - renaming the intermediate assemblies to the final one.

Old plan:

• Remove packages not flowing anywhere #8386
• Add skeleton of single compiler DLL #8395
• Move compiler code into the new project #8471
• Update VSIX on Roslyn side similarly to Add razor compiler EA assembly to VSIX roslyn#67501
• Update transports.
• Update runtime compilation in aspnetcore.
• Delete the old packages.

To allow servicing of the old compiler (branch `release/dev17.6`): Not needed, I think, since we have shims now (#8941)

• [17.6] Remove shared DLL dependency from Razor.Language #8594
• Take dependency on the old compiler in the main branch.

Note To service the old compiler: update the 17.6 branch, release new version of this old package, update main branch to consume that version of the old package, build and insert into VS.

See also:

• Announcement: Razor Compiler API Breaking Changes  #8399

[jaredpar]

Integration tests are blocked on dotnet/dnceng#563