[Fabric] Shim AccessibilityTraits to macOS

[Saadnajmi]

Followup from #2293 :

Appkit doesn't have anything like UIAccessibilityTraits, which React Native uses. We currently do a lossy conversion of the "role" prop to NSAccessibilityRole, where in iOS, the role prop is used to set traits (And RCTAccessibilityTraits), which in turn also is used for things like role and accessibilityValue.

We could improve our accessibility story if we were to implement a shim for UIAccessibilityTraits in RCTUIKit.

[Saadnajmi]

We can maybe take inspiration from https://github.com/ChartsOrg/Charts/blob/master/Source/Charts/Utils/Platform+Accessibility.swift