Both `JudgementCounterDisplay` (via the `ShowMaxJudgement` callback)
and the `JudgementCounter.Pop{In,Out}` methods were operating on the
alpha of the `JudgementCounter`. This meant that if the counter display
was created with max judgement initially hidden, it would be hidden
by the `ShowMaxJudgement` callback first, but then _unhidden_
by `PopIn()`.
Allows directly referencing rather than going through `DrawableRuleset`.
Helps with testing and implementation of the new song progress display
(#22144).