Based on Flutter's `camera_avfoundation` 0.10.3 (BSD license).

Local changes:

- Downscale rear-camera BGRA analysis frames to a maximum edge of 640 pixels
  with Accelerate, before copying them to Dart. Limit delivery to 10 fps.
  Preview textures, video recording, and front-camera frame delivery are unchanged.
- Cover stream resizing with `CameraImageStreamScalerTests`.

The app configures front-camera sessions at 720p and rear-camera sessions at
1080p. The shutter uses the preview screenshot path.