Add ILLink annotations to Microsoft.CSharp

[krwq]

This adds ILLink annotations to Microsoft.CSharp. Majority is RequiresUnreferencedCode.

[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, to 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.

[ghost]

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Issue Details

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This adds ILLink annotations to Microsoft.CSharp. Majority is RequiresUnreferencedCode.

Author:	krwq
Assignees:	-
Labels:	area-Microsoft.CSharp, new-api-needs-documentation
Milestone:	-

[MichalStrehovsky]

Do we want a better message for this than "Types and members might be removed"?

How does the experience look like if I have:

dynamic foo = "Hello";
dynamic bar = "World";
Console.WriteLine(foo + bar);

It would be nice if there was indication that this is caused by the dynamic keyword. Developers who use C# dynamic typically don't know how it's implemented. I've seen code written in ways that very much looked like someone didn't understand the difference between var and dynamic.

[ghost]

Tagging subscribers to 'linkable-framework': @eerhardt, @vitek-karas, @LakshanF, @tannergooding, @sbomer
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Issue Details

---

This adds ILLink annotations to Microsoft.CSharp. Majority is RequiresUnreferencedCode.

Author:	krwq
Assignees:	-
Labels:	area-Microsoft.CSharp, linkable-framework
Milestone:	-

[eerhardt]

Looks like your new trimming test is failing on mono -

Type `System.Runtime.InteropServices.COMException` does not have constructor
The command "/__w/1/s/artifacts/bin/trimmingTests/projects/MarshalGetExceptionForHRTests.TrimmingTests/MarshalGetExceptionForHRTests/browser-wasm/bin/Release/net6.0/browser-wasm/AppBundle/run-v8.sh" exited with code 255.

[krwq]

@MichalStrehovsky I've changed message to Using dynamic types might cause types or members to be removed by trimmer., let me know if you have better idea for wording

[eerhardt]

LGTM. I had just a couple minor comments, once those are addressed I think we should merge this. Thanks for the good work here, @krwq!