It didn't ever really make sense for it to be sharing the implementation
details of that (e.g. colouring of primary/dangerous actions), and with
the hotkey display things got outright hacky, so I'm decoupling it
entirely.
Closes https://github.com/ppy/osu/issues/28750.
Yes this is not the perfect change to fix this (which would probably be
some framework change to take bounds of the parenting input manager into
account). I really do not want to go there and would like to just fix
this locally and move on. Due to the game-wide scaling container this
sorta works for any resolution anyhow.