Add diagnostics for struct initialization errors

[BillWagner]

Fixes #49600

In addition, address feedback on #51329 that was posted after merging:

• Add help for various C# 11 diagnostics #51329 (comment)
• Add help for various C# 11 diagnostics #51329 (comment)
• Add help for various C# 11 diagnostics #51329 (comment)
• Add help for various C# 11 diagnostics #51329 (comment)

The file for constructor errors was also outdated in style, so do a refactoring to focus on how to fix these diagnostics, and apply current styles.

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Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/compiler-messages/constructor-errors.md	Resolve errors and warnings in constructor declarations
docs/csharp/language-reference/compiler-messages/feature-version-errors.md	Resolve warnings related to language features and versions
docs/csharp/language-reference/compiler-messages/source-generator-errors.md	Errors and warnings associated with source generators and interceptors
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

Updates C# compiler diagnostic documentation by consolidating several constructor/struct-initialization errors into the newer themed “constructor declarations” article, updating navigation, and adding redirects from legacy per-error pages.

Changes:

• Moved CS0132, CS0573, and CS1018 guidance into constructor-errors.md, and removed the legacy standalone pages.
• Updated TOC and “no specifics” fallback page to reflect the new diagnostic coverage.
• Added redirects for removed pages, and refreshed wording in related diagnostic theme pages.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 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 dedicated guidance elsewhere.
docs/csharp/misc/cs0573.md	Removes legacy per-error page (replaced by themed article + redirect).
docs/csharp/misc/cs0132.md	Removes legacy per-error page (replaced by themed article + redirect).
docs/csharp/language-reference/toc.yml	Re-points diagnostic navigation to the themed constructor article and removes old entries.
docs/csharp/language-reference/compiler-messages/source-generator-errors.md	Minor wording updates for consistency.
docs/csharp/language-reference/compiler-messages/feature-version-errors.md	Updates the listed CS9041 diagnostic text.
docs/csharp/language-reference/compiler-messages/cs1018.md	Removes legacy per-error page (replaced by themed article + redirect).
docs/csharp/language-reference/compiler-messages/constructor-errors.md	Major refactor and expansion to include additional constructor/struct-init diagnostics.
.openpublishing.redirection.csharp.json	Adds redirects for removed pages to the new themed sections.

Comments suppressed due to low confidence (1)

docs/csharp/language-reference/compiler-messages/constructor-errors.md:188

• This section heading is ## Constructor declaration, which produces the anchor #constructor-declaration. However, several existing redirects target constructor-errors#constructor-declarations (for example, .openpublishing.redirection.csharp.json entries for CS0526, CS0710, and CS0824). Rename this heading to ## Constructor declarations or add an explicit anchor so those redirects continue to land on the intended section.

## Constructor declaration

- **CS0526**: *Interfaces cannot contain constructors.*