Add new API docs for System.Runtime.InteropServices

[jkoritzinsky]

Adds the rest of the missing API docs we can put in code from #105986

@carlossanlop the CollectionsMarshal APIs do have docs in source. Do we need to manually port them to dotnet-api-docs?

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[carlossanlop]

the CollectionsMarshal APIs do have docs in source. Do we need to manually port them to dotnet-api-docs?

@jkoritzinsky Yes, they need them manually ported, because the source of truth is not triple slash comments, but dotnet-api-docs, as indicated by this turned-off property in the csproj:

runtime/src/libraries/System.Runtime.InteropServices/src/System.Runtime.InteropServices.csproj

Line 7 in d756da3

<UseCompilerGeneratedDocXmlFile>false</UseCompilerGeneratedDocXmlFile>

[carlossanlop]

Note: We can't just turn the property on, because we would need to backport the language-reviewed docs from dotnet-api-docs into runtime first.

[jkoritzinsky]

Okay I'll port the docs over manually after this PR gets in.

[carlossanlop]

Left some suggestions for you to consider, and aside from that, it looks good.