Rewrites asx file support using vlc_xml API

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
Resolving XML special chars on xml based format

It fixes bug #9311 and resolves xml special chars on several other xml based playlist format (b4s, podcast, shoutcast, qtl).
Adding "save to playlist" menu item in submenu Recents.

adding RecentsMRL::toPlaylist()
refactoring functions to eliminate repeating code
refactoring public DialogProvider::saveAPlaylist() to private DialogProvider::saveAPlaylist(playlist_t *p_playlist, playlist_item_t *p_node)
and making new DialogProvider::savePlayingToPlaylist() and DialogProvider::saveRecentsToPlaylist()

this commit includes fixes related to Jean-Baptiste Kempf code review.
 - fixing whitespace problem
 - RecentsMRL::toPlaylist null handling

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
Wav: Reject invalid files leading to FPE