Add additional memory safety diagnostics

[BillWagner]

Fixes #54012

Add the additional memory safety related diagnostics.

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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/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 mapping for new and existing memory-safety and unsafe-code diagnostics by consolidating several compiler error/warning codes into the centralized Unsafe code diagnostics page, updating F1 keyword routing, and adding redirects for removed standalone pages.

Changes:

• Move/centralize additional unsafe/memory-safety diagnostics (including newer C# 15 “unsafe evolution” codes) into unsafe-code-errors.md with updated keyword mappings.
• Remove standalone pages for CS1664 and CS8500, and add redirects to the consolidated unsafe diagnostics page.
• Update the “Sorry, we don’t have specifics…” catch-all list and the C# language reference TOC/displayName mapping to reflect the new routing.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md	Removes diagnostics that now have coverage via the unsafe diagnostics hub page.
docs/csharp/misc/cs8500.md	Deletes the standalone CS8500 page in favor of consolidated coverage.
docs/csharp/misc/cs1664.md	Deletes the standalone CS1664 page in favor of consolidated coverage.
docs/csharp/language-reference/toc.yml	Updates the unsafe-code node displayName list and removes the CS1664 standalone TOC entry.
docs/csharp/language-reference/compiler-messages/unsafe-code-errors.md	Adds keyword routing and guidance for additional unsafe/memory-safety diagnostics.
.openpublishing.redirection.csharp.json	Adds redirects from removed standalone pages to the consolidated unsafe diagnostics page.

Comments suppressed due to low confidence (1)

docs/csharp/language-reference/compiler-messages/unsafe-code-errors.md:302

• There are two consecutive blank lines at the end of the file, which can trigger markdownlint MD012 (multiple consecutive blank lines). Remove the extra trailing blank lines.

To get a function pointer, use the address-of operator with an explicit function pointer type cast. Don't use the [address-of operator `&`](../operators/pointer-related-operators.md#address-of-operator-) to assign method groups to `void*` or other non-function pointer types. For more information, see [Function pointers](../unsafe-code.md#function-pointers).