Fixes #5233: Enhance MCP image handling with robust validation and security controls

- Enhanced accessMcpResourceTool.ts with comprehensive image validation
- Added magic byte checking for JPEG, PNG, GIF, WebP, and BMP formats
- Implemented security controls for max images per response and max image size
- Added VSCode settings for mcpMaxImagesPerResponse and mcpMaxImageSizeMB
- Added localization strings for new settings
- Created comprehensive test suite with 12 test cases covering:
  - Image format validation (JPEG, PNG, GIF, WebP, BMP)
  - Corrupted image detection
  - Security limit enforcement
  - Mixed content handling
  - Error handling and edge cases
  - Configuration management
- All tests passing with robust error handling and graceful degradation

Author: roomote