Add xref links to new .NET 11 Preview 2 APIs in what's-new docs

[Copilot]

New .NET 11 APIs introduced in Preview 2 were referenced as plain backtick text in libraries.md instead of xref links. Updates three locations:

• ZipCompressionMethod enum members: Stored, Deflate, and Deflate64 now link to System.IO.Compression.ZipCompressionMethod.*
• StringSyntaxAttribute language constants: CSharp, FSharp, and VisualBasic now link to System.Diagnostics.CodeAnalysis.StringSyntaxAttribute.* with nameWithType
• JsonSerializerOptions generic methods: Inline text for GetTypeInfo<T> and TryGetTypeInfo<T>() now use full xrefs with generic type parameter encoding:

  <xref:System.Text.Json.JsonSerializerOptions.GetTypeInfo``1?displayProperty=nameWithType>
  <xref:System.Text.Json.JsonSerializerOptions.TryGetTypeInfo``1(System.Text.Json.Serialization.Metadata.JsonTypeInfo{``0}@)?displayProperty=nameWithType>
  

Note: SVE2 intrinsics (ShiftRightLogicalNarrowingSaturate) mentioned in runtime.md are not yet published to dotnet/dotnet-api-docs and remain unlinked.

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Internal previews

📄 File	🔗 Preview link
docs/core/whats-new/dotnet-11/libraries.md	What's new in .NET libraries for .NET 11

[Copilot]

Pull request overview

This PR updates the .NET 11 “what’s new” libraries documentation to replace inline backticked API names with <xref:...> links so readers can navigate directly to the relevant API reference entries.

Changes:

• Link ZipCompressionMethod enum members (Stored, Deflate, and Deflate64) via xrefs.
• Link StringSyntaxAttribute language constants (CSharp, FSharp, and VisualBasic) via xrefs.
• Link JsonSerializerOptions generic metadata methods (GetTypeInfo<T> and TryGetTypeInfo<T>) via xrefs.

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[BillWagner]

This LGTM. Let's