Move React Native Environment Mocks to root (#8963)

These mocks are things we expect to be available in the React Native
environment. I'd like to move them out of the renderer folder so that we
can sync that folder to React Native as is without overriding its mocks.

I motivate by the fact that they're not really part of the renderer code
itself. I leave the ReactNative mock since that is in fact part of the
renderer.

Author: sebmarkbage