Switch to MediaPlaybackItem for queues and playback

[YourOrdinaryCat]

Resolved / Related Issues Items resolved / related issues by this PR.

• Closes #178

Details of Changes The app currently uses the IMediaItem interface (implemented by SongViewModel and VideoViewModel) to handle media playback and information about currently playing media. However, this is problematic due to the conversions that have to happen between IMediaItem and MediaPlaybackItem to be able to start media playback. With the current architecture, any scenario where the app has to play media directly from a StorageFile (e.g drag & drop, file associations) is not possible unless the file is coming from the user's library, which isn't always the case.

• Added methods to handle playback and queues without the need for IMediaItem
• Fixed thumbnails in now playing - the thumbnail is now fetched directly from the file when playing it, which means higher quality and allows displaying unique thumbnails for every song, even if they're on the same album (closing #178)

Validation

• [x] Check if all needed metadata for playing/queued media is displayed
• [x] Make sure thumbnails are working as intended in Now Playing
• [x] Make sure the following scenarios are functioning as intended:
• • [x] Online playback
• • [x] Drag & drop
• • [x] File association

Screenshots / Videos (optional) HQ thumbnails in Now Playing:

[itsWindows11]

Also it should show "Unknown Artist" for unrecognized artists and hide that for videos.

[itsWindows11]

Playing music then playing a video seems to crash the app with a null reference exception.

[YourOrdinaryCat]

Playing music then playing a video seems to crash the app with a null reference exception.

Can't reproduce here, got exception logs? Or maybe more concrete steps, just playing a song then a video works fine here.

[itsWindows11]

Nevermind, fixed it myself, this PR can be merged as-is now.