Annotate Microsoft.CSharp with RequiresDynamicCode

[agocke]

The public API surface looks exactly like RequiresUnreferencedCode, but the private implementation details vary slightly. I don't think there's a meaningful difference in the annotations for RDC vs RUC.

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[dotnet-issue-labeler]

Note regarding the new-api-needs-documentation label:

This serves as a reminder for when your PR is modifying a ref *.cs file and adding/modifying public APIs, please make sure the API implementation in the src *.cs file is documented with triple slash comments, so the PR reviewers can sign off that change.

[Copilot]

Copilot reviewed 64 out of 65 changed files in this pull request and generated no comments.

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• src/libraries/Microsoft.CSharp/src/Microsoft.CSharp.csproj: Language not supported

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[sbomer]

LGTM, thanks!