Improve function descriptions

[JonasHelming]

Improves AI tool descriptions to provide better guidance for the Coder agent, hopefully resulting in more effective tool usage and fewer errors.

Key improvements:

• runTask/listTasks: Added output format details, examples, and cross-references
• *FileReplacements: Added failure recovery guidance explaining "Expected 1 found X" errors
• searchInWorkspace: Made 30-result limit prominent, added "when NOT to use" guidance
• getFileDiagnostics: Documented severity filtering (Error/Warning only) and language service timing
• findFilesByPattern: Added performance warning and subdirectory optimization advice
• All tools: Standardized parameter descriptions with examples and added "when to use" alternatives

How to test

1. Use the Coder agent in agent mode
2. Verify the agent makes better tool choices (e.g., uses findFilesByPattern for file discovery, searchInWorkspace for content search)
3. Verify the agent recovers better from replacement failures by re-reading files and adjusting oldContent

Follow-ups

Breaking changes

• This PR introduces breaking changes and requires careful review. If yes, the breaking changes section in the changelog has been updated.

Attribution

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines
• User-facing text is internationalized using the nls service (for details, please see the Internationalization/Localization section in the Coding Guidelines)

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[planger]

I just did some vibe testing. Seems to work fine! Let's give it a spin in practice, thank you!