Fix screen offsetting not handling scaled game instances
Fix screen offsetting not handling scaled game instances

By using `Content` instead, now the logic will get the X of the settings
overlay at the `Content` space, which can be scaled in the
`ScalingMode.Everything` mode.

And in the case of `ScalingMode.ExcludeOverlays`, a subcontainer
somewhere inside `Content` that's holding the screen stack would be scaled,
but `Content` won't be affected which is what we want in that case.

ppy/osu,peppy/osu-new,smoogipooo/osu,ppy/osu,NeoAdonis/osu,peppy/osu,smoogipoo/osu,smoogipoo/osu,ppy/osu,smoogipoo/osu,peppy/osu,NeoAdonis/osu,peppy/osu,NeoAdonis/osu