macosx: Add a new table view for the audio library's 'Songs' section, refactor audio view management

The previous splitview implementation, which was previously shared by all audio library sections when in list view mode, was incomplete for songs with an unused space on the right-hand-side.

Rather than trying to mangle this layout to work for songs, a better approach is to offer a more traditional table view for all of the user's songs, much like established music players do.

This PR implements such a table view:

Screen_Recording_2022-12-03_at_15.21.31

This PR also contains a refactor of the library window's audio-library-related responsibilities, extracting them into a dedicated VLCLibraryAudioViewController

Signed-off-by: Claudio Cambra developer@claudiocambra.com