Add module initializer diagnostics

[BillWagner]

Fixes #52836

Added the module initializer diagnostics to the file with constructor diagnostics.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/compiler-messages/constructor-errors.md	Resolve errors and warnings for constructor declarations and module initializers
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 addresses dotnet/docs issue #52836 by moving C# 9 module initializer diagnostics out of the “no specifics” placeholder page and into the existing constructor diagnostics article, plus updating navigation/search metadata to point to the new location.

Changes:

• Removed module initializer-related f1_keywords entries (CS8813–CS8816, CS8900–CS8902) from the generic “sorry” error page.
• Updated the C# language-reference TOC entry to reflect module initializer coverage and include the relevant diagnostic IDs in displayName.
• Expanded constructor-errors.md to include module initializer diagnostics (metadata + a new “Module initializer declarations” section), and updated title/description/date accordingly.

Reviewed changes

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

File	Description
docs/csharp/misc/sorry-we-don-t-have-specifics-on-this-csharp-error.md	Removes module initializer diagnostic IDs now documented elsewhere.
docs/csharp/language-reference/toc.yml	Renames the constructors TOC node and adds module initializer diagnostic IDs for discoverability.
docs/csharp/language-reference/compiler-messages/constructor-errors.md	Adds module initializer diagnostics and guidance, and updates metadata/title to reflect expanded scope.