VolumeMeter
ScrollDelta
IsPrecise
var
Closes https://github.com/ppy/osu/issues/13761.
bool
Also refactors the whole method to generally clean things up. One more important fix is setting the frequency on the channel before starting playback, so avoid the frequency potentially being adjusted after the playback is already started.
Also cleans up some weird code
Use IMouseWheelBindingHandler for volume VolumeControlReceptor. VolumeMeter is no longer an IKeyBindingHandler because it is unused.