[React] Fix getEventModifierState in Chrome

Summary: When returning event.getModifierState directly it loses the context of the native event which results in an IllegalInvocation error in Chrome. This fixes it by always wrapping the function and by calling `getModifierState` on the native event.

Test Plan: In Chrome, I invoked `event.getModifierState('Alt')` in an onKeyDown event. It throws without the fix and works fine with the fix applied.