Ensure modal size changes correctly when orientation changes

[hsource]

Motivation

Users of our app (that had recently switched to react-native-multiple-modals) noticed that the modal had the wrong sizes in some cases:

1. When starting the app in landscape, the orientation was incorrect
2. When opening the modal after rotating, the orientation would also become incorrect

Investigation/root cause

1. Right now, we call RCTScreenSize and invert the size if it's in landscape. This isn't needed and causes the initial dimensions to be inverted because RCTScreenSize already takes into account the orientation
2. For unknown reasons, RNTModalViewController's viewDidAppear never seems to get called on Paper, which makes it so that shouldTrackRotationChange never gets set to true. This also seems not to be really needed and isn't used in the React Native equivalent RCTModalHostViewController.m

Fix

1. Just call RCTScreenSize without processing the output, since it already accounts for screen orientation
2. Get rid of shouldTrackRotationChange

Testing

Note: I only tested on Paper since our app is on an old, non-Fabric RN version

In the before version, the scrim doesn't cover the correct part of the screen because the shadow view width is incorrect.

Before	After

[paufau]

Thanks for noticing the issue and submitting a pull request!

It will take some time for me to test it on the new architecture and other devices.

[paufau]

Sorry for the long delay. The fix works perfectly on Fabric!
So, I'm going to merge it and release asap.

Thank you a lot!