Add missing media3 Stub OnPositionDiscontinuity back to Android Med… (#2825)

* Add missing media3 Stub `OnPositionDiscontinuity` back to Android MediaManager class

* Add OnMetadata method to MediaManager.android.cs

Introduced a new method `OnMetadata(Metadata? metadata)`
to handle updates related to media metadata in the
MediaManager.android.cs file.

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Co-authored-by: Brandon Minnick <[email protected]>

Author: ne0rrmatrix

src/CommunityToolkit.Maui.MediaElement/Views/MediaManager.android.cs

@@ -733,7 +733,9 @@ public void OnLoadingChanged(bool isLoading) { }
 	public void OnMaxSeekToPreviousPositionChanged(long maxSeekToPreviousPositionMs) { }
 	public void OnMediaItemTransition(MediaItem? mediaItem, int reason) { }
 	public void OnMediaMetadataChanged(MediaMetadata? mediaMetadata) { }
+	public void OnMetadata(Metadata? metadata) { }
 	public void OnPlayWhenReadyChanged(bool playWhenReady, int reason) { }
+	public void OnPositionDiscontinuity(PlayerPositionInfo? oldPosition, PlayerPositionInfo? newPosition, int reason) { }
 	public void OnPlaybackSuppressionReasonChanged(int playbackSuppressionReason) { }
 	public void OnPlayerErrorChanged(PlaybackException? error) { }
 	public void OnPlaylistMetadataChanged(MediaMetadata? mediaMetadata) { }