Document IL2125 and IL3058 transitive reference compatibility warnings

[Copilot]

Summary

Documents new analyzer warnings IL2125 and IL3058 introduced in dotnet/runtime#118180 for verifying transitive dependency compatibility with trimming and Native AOT.

New warning documentation:

• IL2125: Referenced assembly is not annotated for trim compatibility - emitted when VerifyReferenceTrimCompatibility=true and a referenced assembly lacks IsTrimmable metadata
• IL3058: Referenced assembly is not annotated for AOT compatibility - emitted when VerifyReferenceAotCompatibility=true and a referenced assembly lacks IsAotCompatible metadata

Updated conceptual documentation:

• Added VerifyReferenceTrimCompatibility property to trim preparation guide
• Added VerifyReferenceAotCompatibility property to Native AOT overview
• Added note that IsAotCompatible metadata was introduced in .NET 10

Documentation approach:

• Uses consistent terminology: "annotated for trim/AOT compatibility" throughout
• Provides two options to fix violations: update the library or disable verification
• Does not suggest warning suppression (these warnings cannot be suppressed at source location)

Both properties are opt-in, allowing library authors to enforce that all dependencies explicitly declare trim/AOT compatibility:

<PropertyGroup>
  <IsTrimmable>true</IsTrimmable>
  <VerifyReferenceTrimCompatibility>true</VerifyReferenceTrimCompatibility>
</PropertyGroup>

Original prompt

Clone dotnet/runtime#118180 and inspect the changes. Then write documentation for the new feature.

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