[native/lib] introduce useENSResolvedAvatar hook in avatar-utils

Summary:
This logic will need to be used in both UserAvatars and ThreadAvatar, so I factored out the logic to easily reuse in both cases.

Depends on D7259

Test Plan: Same test plan as D7246, and all user avatars still render correctly

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7260