feat(util, executor, translator): enhance Antigravity schema handling and response formatting

- Introduced `CleanJSONSchemaForAntigravityResponse` to process schemas without adding tool-specific placeholders.
- Updated `cleanJSONSchema` with `removeGeminiMetadata` parameter for improved schema control.
- Refactored Antigravity schema sanitization to handle declaration and generation paths independently.
- Mapped OpenAI `response_format` to Antigravity settings, ensuring proper response schema cleaning.
- Expanded tests to verify proper placeholder-free response schema handling and metadata preservation.

Closes: #4652