[native] Move UserAvatar "inside" EditUserAvatar

Summary:
Intead of passing in UserAvatar as React.Node as a prop to EditUserAvatar, we pass ?userID as a prop and render UserAvatar "inside" EditUserAvatar.

Depends on D7507

Test Plan:
Things continue to look and work as expected:

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7508