[camera_avfoundation] Adds support for video stabilization

[ruicraveiro]

Implements getSupportedVideoStabilizationModes() and setVideoStabilizationMode() methods in AVFoundationCamera.

Address issue flutter/flutter#89525.
It is the camera_avfoundation sub-PR for #7108.

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[gemini-code-assist]

Code Review

This pull request adds support for video stabilization, which is a great new feature. The implementation looks solid across Dart, Swift, and Objective-C. I've found a minor issue in the Dart implementation related to a copy-paste error in a comment and a suggestion for a safer fallback value for forward compatibility. The rest of the changes, including the native implementation and tests, are well done.

[gemini-code-assist]

There are a couple of improvements that can be made in this method:

1. The documentation comment appears to be a copy-paste error and refers to ResolutionPreset instead of VideoStabilizationMode.
2. The fallback return value for unknown VideoStabilizationMode values is PlatformVideoStabilizationMode.cinematic. It would be safer to return null here. The function has a nullable return type, and the calling method _getSupportedVideoStabilizationModeMap already handles null by correctly treating the mode as unsupported. This would prevent new enum values from being incorrectly mapped to cinematic mode.

  /// Returns a [VideoStabilizationMode]'s Pigeon representation.
  PlatformVideoStabilizationMode? _pigeonVideoStabilizationMode(
    VideoStabilizationMode videoStabilizationMode,
  ) {
    switch (videoStabilizationMode) {
      case VideoStabilizationMode.off:
        return PlatformVideoStabilizationMode.off;
      case VideoStabilizationMode.level1:
        return PlatformVideoStabilizationMode.standard;
      case VideoStabilizationMode.level2:
        return PlatformVideoStabilizationMode.cinematic;
      case VideoStabilizationMode.level3:
        return PlatformVideoStabilizationMode.cinematicExtended;
    }
    // The enum comes from a different package, which could get a new value at
    // any time, so provide a fallback that ensures this won't break when used
    // with a version that contains new values. This is deliberately outside
    // the switch rather than a `default` so that the linter will flag the
    // switch as needing an update.
    // ignore: dead_code
    return null;
  }