Add interpolated string handler error diagmostics

[BillWagner]

Fixes #51442

Add a new file with all diagnostics related to interpolated strings.

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Internal previews

📄 File	🔗 Preview link
.github/prompts/error-consolidation.md	Copilot prompts to consolidate error codes.
docs/csharp/language-reference/compiler-messages/ref-modifiers-errors.md	Errors and warnings associated with reference parameters, variables, and returns
docs/csharp/language-reference/compiler-messages/string-interpolations.md	Resolve errors and warnings for string interpolation expressions
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 adds a dedicated compiler-messages article for string interpolation–related diagnostics (including interpolated string handler diagnostics) and updates navigation and the “undocumented errors” list accordingly.

Changes:

• Add string-interpolations.md covering multiple interpolation- and handler-related diagnostics.
• Update docs/csharp/language-reference/toc.yml to include the new “String interpolations” entry.
• Remove newly documented diagnostics from sorry-we-don-t-have-specifics-on-this-csharp-error.md.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

File	Description
docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md	Removes several diagnostic codes that are now documented elsewhere.
docs/csharp/language-reference/toc.yml	Adds a TOC entry for the new string interpolation diagnostics article.
docs/csharp/language-reference/compiler-messages/string-interpolations.md	New consolidated diagnostics page for string interpolations and interpolated string handlers.
.github/prompts/error-consolidation.md	Updates the consolidation prompt’s target file and theme to string interpolations/handlers.