Add design usage notes to TypeMapAttribute and TypeMapAssociationAttribute documentation

[Copilot]

• Add detailed Remarks section to TypeMapAttribute<TTypeMapGroup> class documentation with:
  • Usage explanation for type mapping between strings and types
  • Trimming rules for External Type Map
  • List of IL instructions that trigger type map entry inclusion
• Add detailed Remarks section to TypeMapAssociationAttribute<TTypeMapGroup> class documentation with:
  • Usage explanation for type associations between source and proxy types
  • Trimming rules for Proxy Type Map
  • List of IL instructions that trigger type association entry inclusion
• Fixed typo in constructor parameter description
• Improved readability per code review feedback
• Applied PR review suggestions: use xref format for type references
• Fixed TypeMapAssemblyTarget xref (removed Attribute suffix per review)
• Changed "it's not" to "isn't" for consistent conversational tone

Original prompt

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This section details on the original issue you should resolve

<issue_title>TypeMapAttribute/TypeMapAssociationAttribute Add design usage notes to documentation</issue_title>
<issue_description>Design details and usage requirements should be pushed into the "Remarks" section of the two APIs.

https://learn.microsoft.com/dotnet/api/system.runtime.interopservices.typemapassociationattribute-1
https://learn.microsoft.com/dotnet/api/system.runtime.interopservices.typemapattribute-1

The design details can be found at https://github.com/dotnet/runtime/blob/main/docs/design/features/typemap.md.</issue_description>

<agent_instructions>The primary data in the design doc are the bulleted list for how the attributes influence trimming logic.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@AaronRobinsonMSFT /cc @Sergio0694 @AaronRobinsonMSFT /cc @jkoritzinsky @jtschuster @sbomer @agocke @MichalStrehovsky

• Fixes TypeMapAttribute/TypeMapAssociationAttribute Add design usage notes to documentation #12102

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[Copilot]

Pull request overview

This PR adds comprehensive design documentation to the TypeMapAttribute<TTypeMapGroup> and TypeMapAssociationAttribute<TTypeMapGroup> classes, documenting their trimming behavior based on the runtime design specification. The documentation clarifies how these attributes influence trimming logic for interop scenarios.

Key changes:

• Added detailed Remarks sections explaining External Type Map and Proxy Type Map behavior during trimming
• Documented specific IL instructions that trigger map entry inclusion (e.g., ldtoken, unbox, isinst, castclass, box, newarr, newobj)
• Fixed a typo in the TypeMapAttribute constructor parameter description ("kthe" → "the")

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
xml/System.Runtime.InteropServices/TypeMapAttribute`1.xml	Adds Remarks section documenting unmanaged-to-managed interop type mapping behavior, lists IL instructions triggering External Type Map inclusion, and fixes typo in constructor parameter
xml/System.Runtime.InteropServices/TypeMapAssociationAttribute`1.xml	Adds Remarks section documenting managed-to-unmanaged interop proxy type associations, lists IL instructions triggering Proxy Type Map inclusion, and explains special handling for interface types with IDynamicInterfaceCastable

[AaronRobinsonMSFT]

/cc @gewarren

[AaronRobinsonMSFT]

@copilot Please apply comment feedback.

[gewarren]

lgtm

[AaronRobinsonMSFT]

Looks like there is some formatting issues. I'll put up another PR and fix them up.