There should be a way to be able to search songs/artist within your playlists all at once. My proposition at how this could be done is by having the option to click on a song from your library and having the option to see what saved playlists it can be found within. You could also implement a new search filter within the global search that shows what saved playlists the song is within. This could also be done with artists and would have the same functionality. It is almost similar to the Discovered On tab which can be found in an artist's about section. Thank you, for your time.