This is quite a breaking change, but I think it is beneficial due to the large amount of usage of this class.
I originally intended just to remove the allocations of the two delegates handling the `Changed` flow internally, but as nothing was really using the bindables for anything more than a general "point has changed" case, this felt like a better direction.
Closes https://github.com/ppy/osu/issues/10672.
In two minds about how this should be implemented but went in this
direction initially. The other way would be to add local handling of
Shift-Right Click inside PathControlPointPiece (which is already doing
mouse handling itself).