See T348286: Move the default OOUI overlay and window manager inside the MediaWiki teleport target.
This is the same idea, but for the custom OOUI overlays and window managers created by VisualEditor. We don't use the default ones in VE (almost?) anywhere.
We'll need to introduce some API in standalone VE to use instead of the MW teleport target, since it's not available there.
As a result, we should be able to remove the various hacky uses of 'vector-body', and maybe delete some skinStyles currently applied for Vector.