lib: rework LibVLC 4.0 API
Changelog (since https://code.videolan.org/tguillem/vlc/-/commits/libvlc-new-apis-rebase-thumb)
- Removed redundant commit 'lib: add media_player synchronisation functions' (already upstreamed)
- Added versioned callbacks in media and media discoverer tests
- Parser rework (with adapted tests)
- Thumbnailer rework (with adapted tests)