Internals: rework FocusScope system, current scope doesn't need to be in window + child doesn't inherit.

Intended as part of work for input routing + blind menu processing shortcuts. Some of this commit will be stripped by next commit.
Intent was to sort windows along with focus scope to build a hierarchy, but for our needs we'd need a persistant one, so scrapping the idea. Not squashing this with next commit to keep a bit of history for future references.
4 files changed