Using source generators for interop

[JeremyKuhne]

This issue is for tracking usage of source generators for interop.

The Runtime is considering implementing P/Invoke support through source generators: https://github.com/dotnet/runtime/blob/master/docs/design/features/source-generator-pinvokes.md

We should also be exploring is implementing common patterns via source generators. Things like:

• Handling common buffer usage patterns (buffer growth, movement from stack to heap, etc.)
• Generating resource scoping boilerplate (see our various scope types and how we switch between class and struct for tracking proper disposal in debug builds)

[JeremyKuhne]

Related issues/pulls:

https://github.com/dotnet/runtime/pull/32091

[elachlan]

@RussKie Should we close this issue because of #7445?

[RussKie]

Yes, thank you for finding this.