Use IMouseWheelBindingHandler for volume VolumeControlReceptor. VolumeMeter is no longer an IKeyBindingHandler because it is unused.
Add a default ruleset to `OsuTestCase` to cover testing scenarios.
Also decouples the bindable at SongSelect, where it is debounced in line with the carousel being updated.
OnMouseMove isn't invoked when hover is lost.
# Conflicts: # osu.Game.Tests/Visual/TestCaseChatLink.cs