Add comment and reduce how often `ChildrenOfType` is invoked in `ExpandingButtonContainer`
Add comment and reduce how often `ChildrenOfType` is invoked in `ExpandingButtonContainer`

ppy/osu,NeoAdonis/osu,ppy/osu,NeoAdonis/osu,peppy/osu,NeoAdonis/osu,peppy/osu,peppy/osu,ppy/osu