As a user, I'd like the ability to add individual songs to my library from albums, playlists, or the artist pages without marking them as liked songs or adding a whole album to my library. Doing this would allow me to navigate to that artist in my library, and then listen to all the songs I've saved by them and for the ones I especially liked, I can "heart" those as liked songs.
Example: An artist has an album with 20 tracks. Of the 20, I typically listen to 5 tracks. I want to have the ability to add each of those 5 songs to my library without liking them. When I want to listen, I search for the artist, scroll to the respective album, and I only see those 5 songs to play from the album in my library.