Fix footer buttons still being able to fire their action when temporarily hidden by overlay content

[bdach]

In human words: I read this forum thread today and was horrified to see the user there opening the F3 options menu in song select when the F1 mod overlay was pulled up, which is (a) not intended UX, (b) looks terrible, and (c) just wrecks the game behaviourally wholesale from start to end.

So with this change you don't get to open options via F3 while inside mod overlay at all.

The Action shadowing is pretty ugly but I don't have better ideas. Initially I tried to mess with Enabled (as I did once previously, see 36628e2), but it's much more complicated in this case because the enabled state needs to be restored when the buttons reappear, or it could change independently while the buttons are temporarily hidden, etc. So I'd rather just not deal with all that and invent a parallel scheme.

[LiquidPL]

I have a branch where I've been working on cleaning up the footer, and it happens to have this issue fixed through:

• making a custom container for the footer buttons which doesn't try to relayout everything when a button is moved up/down, which then leads to
• getting rid of the whole 'actually we're animating a container nested inside the button drawable' thing

All of it makes it so that once a button gets animated off the screen it just automatically stops being considered for inputs as it should¹.

The branch in question is somewhat large since it refactors the footer logic away from ScreenFooter to OsuScreen like i mentioned on discord back in Feburary. I'm not sure if there's a point in backporting that small part concerning the buttons to the current ScreenFooter but I wanted to mention that I have something for this already.

Footnotes

1. It doesn't fix it completely, since there's still a short amount of time while the button is animated away where a user could quickly mash [F3] into some number to activate something in the options menu, breaking the game anyway. ↩

[peppy]

A bit ugly bit will do