[native] Animate opacity and scale of ReactionSelectionPopover

Summary:
First step to animating this along with tooltip components

Depends on D7011

Test Plan: Flow, and testing the reaction popover animation on iOS and Android release builds, including opening the emoji keyboard

Reviewers: ginsu

Reviewed By: ginsu

Subscribers: tomek, atul

Differential Revision: https://phab.comm.dev/D7012