Add diagnostics for new unsafe contract errors

[BillWagner]

Fixes #51989

Add new C# errors for Unsafe evolution. Search for other related errors and warnings.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/compiler-messages/unsafe-code-errors.md	Resolve errors and warnings in unsafe code constructs
docs/csharp/language-reference/toc.yml	docs/csharp/language-reference/toc
docs/csharp/misc/cs1654.md	Compiler Error CS1654
docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md	Coming in C# 15

[Copilot]

Pull request overview

This PR updates the C# documentation to cover new “unsafe evolution” compiler diagnostics by routing the relevant error codes to the existing unsafe-code diagnostics article and surfacing them in the language reference TOC.

Changes:

• Move CS7092 and CS8372 out of the generic “no specifics” list and into the unsafe-code diagnostics article.
• Expand unsafe-code-errors.md to include new Unsafe evolution diagnostics (CS9360–CS9377) and reorganize sections to better group fixed-statement vs. unsafe-context guidance.
• Update the C# language reference TOC to include the newly documented diagnostics under the “Unsafe code” entry.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md	Removes CS7092 and CS8372 now that they’re documented elsewhere.
docs/csharp/language-reference/toc.yml	Adds new unsafe-related diagnostic codes to the “Unsafe code” TOC displayName list.
docs/csharp/language-reference/compiler-messages/unsafe-code-errors.md	Documents new unsafe evolution diagnostics and reorganizes sections/keyword lists.