Implement useSizeClassIOS hook

[Saadnajmi]

Platforms Impacted

• iOS
• macOS
• win32 (Office)
• windows
• android

Description of changes

Note, this depends on #1952 landing. This should resolve some issues with #1934

Implement a hook to "guess" the app's size class (if we're running on iOS, undefined on other platforms). We don't have access to this information without a native module / changes in RN Core, so the guess will have to do for now :/

Verification

Updated FluentTester to change to the mobile layout if we're in compact mode.

Simulator.Screen.Recording.-.iPad.Pro.12.9-inch.5th.generation.-.2022-08-03.at.14.10.05.mp4

Pull request checklist

This PR has considered (when applicable):

• Automated Tests
• Documentation and examples
• Keyboard Accessibility
• Voiceover
• Internationalization and Right-to-left Layouts

[Saadnajmi]

We don't want to publicly export this method, so we'll close this in favor of locally implementing / duplicating the code in #1934