When the visualization is set to "Album Cover", the player will now try
to load the embedded image. On failure, it defaults to a "Cover" image
file in the directory.
In Player::play_file_path, file_name_changed now needs to be executed
after that the loader have been set, to get the correct image.
Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).
No functional changes.
Visualization widgets should only have to tell how many samples they
need per frame and have a render method which receives all data relevant
to draw the next frame.
