MediaPlayer: add .pls playlist support

* Add PlaylistFileReader class and derived M3uReader and PlsReader classes.
* Move most of the code from Playlist::AppendM3uToPlaylist to PlaylistFileReader::_AppendItemToPlaylist
* For each File line in the .pls file, a PlaylistItem is added to the MediaPlayer playlist.
* For each Title/Length line, the data is applied to the most recently added PlaylistItem.
* The NumberOfEntries and Version lines are read to make them available for future use, but currently they have no effect.
* Fixes #6813

Change-Id: Ifa23d0df2e4d5b466aa7b85649a78276cff986ef
Reviewed-on: https://review.haiku-os.org/c/haiku/+/5201
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>