[native] Move some types from avatar-selection.react.js to registration-types.js

Summary:
Going to use these types in a new place, so figured it would be better to export them from the shared types file

Depends on D8087

Test Plan: Flow

Reviewers: atul, ginsu

Reviewed By: atul

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8088