[native] Support displaying encrypted avatars

Summary:
Added possibility to display encrypted image avatars on native.

Depends on D9170

Test Plan:
Encrypted avatars that I set on the web (previous diffs) are now displaying on native.
Confirmed that other avatars (both image and emoji) are still displaying correctly.
Tested in user tab, in chat and on chat list (both thread and user avatars).

Reviewers: atul, ginsu

Reviewed By: atul, ginsu

Subscribers: ashoat, tomek, wyilio

Differential Revision: https://phab.comm.dev/D9668