Commit #142418 hid the navigation gizmo and text overlays while in Full
Screen Area by just not allowing those operations while in that mode.
This PR undoes that and instead selectively hides those items and
restores them afterward if they had been showing. The difference is
that this makes it possible to optionally bring them back while in the
mode. This adds a new fullscreen_flag to bScreen to store what was
visible to allow restoring afterward.
Pull Request: https://projects.blender.org/blender/blender/pulls/143144
bbfc42fbf7