Switch razor tooling to use source generator

[chsienki]

Today, the razor tooling hosts its own copy of the compiler APIs, which it uses to generate documents, which are then injected into the Roslyn workspace. The razor source generator is explicitly disabled to allow this.

This has the unfortunate side-effect that when performing an initial hot reload edit, the generator must start from scratch, which is slow.

If we change the tooling to instead 'pull' documents from the Roslyn workspace that are created by the source generator, we can have the 'warmed up' for the first hot reload. This should also remove some complexity from the tooling (and Roslyn) as it will no longer be responsible for injecting the files into the Roslyn workspace.

[chsienki]

Dupe of #6919