We have a lot of code in FlutterViewController that is getting size information from the Flutter view, but scale from the UIScreen. This adds complexity, especially with the deprecation of mainScreen, and it's not at all clear to me what we are involving the screen at all; if we want the Flutter view's scale factor, which I believe is the case, we should use the view's contentScaleFactor.

I don't know for certain that there isn't some subtle reason this is better, vs just an API oversight, but we should investigate to see and simplify the code if it's not necessary to do it this way.