Adds `setImageQuality(int quality)` (1-100 scale) across the camera
plugin ecosystem to allow developers to control JPEG compression
quality for still image capture. Users who do not call setImageQuality
retain the platform's native default behavior.

Implementation details per platform:
- Platform interface: abstract method + method channel implementation
- App-facing: CameraController.setImageQuality with range validation
- Android (Camera2): JpegQualityFeature using CaptureRequest.JPEG_QUALITY
- Android (CameraX): Recreates ImageCapture with Builder.setJpegQuality,
  preserving locked capture orientation
- iOS (AVFoundation): EXIF-preserving JPEG recompression via
  CGImageSource/CGImageDestination (ImageIO), gated on JPEG format only