feat(fabric): Add macOS host platform to ReactCommon

[Saad Najmi (Saadnajmi)]

Summary:

Add a new macOS host platform folder, with overrides for some of the HostPlatform* files to implement some macOS only props. This follows the pattern in React Native Core that Android uses, and what React Native Windows does.

Some notes:

• I also needed to fix a casting issue in RCTPullToRefreshViewComponentView.mm. This is later fixed upstream so we can remove the diff then.
• These new props are not implemented on the component (RCTViewComponentView yet, that will be in a future PR)

Test Plan:

CI should pass.

[Saad Najmi (Saadnajmi)]

Another Q: Should we exclude the cxx platform files from our build?
AKA stuff like: `packages/react-native/ReactCommon/react/renderer/components/view/platform/cxx/react/renderer/components/view/HostPlatformTouch.h

They're all files that most just namespace the base class, so they're safe to compile.

namespacefacebook::react {
using HostPlatformFoo= BaseFoo;
} // namespace facebook::react

The annoying part is they both show up in Xcode and it's hard to tell which one you want to edit. The counterargument would be that we would have different files included in our build for iOS vs macOS which might make building more annoying