Improve SwiftUIWrapperView performance

[bryankeller]

Details

This is a follow-up to #320.

I made the mistake of only testing with a simple view during my performance investigation, which led me to believe that setting the hosting controller's rootView to an Any(EmptyView()) when it went off screen was the best way to get appearance callbacks to work. Although that approach was faster than removing the hosting controller's view from the hierarchy for a very simple view, it gets slower the more complicated the view is. Even a simple Text with a background shape is 10% slower if we set the rootView to an Any(EmptyView()) vs. just removing the hosting controller's view from the hierarchy.

I'm assuming this is the case because it's more expensive to tear down and set up a complicated view from scratch vs. whatever price we pay for removing and adding subviews dynamically.

Related Issue

N/A

Motivation and Context

Performance improvements

How Has This Been Tested

Example app, Airbnb app