[native] switch all user avatars to use UserAvatar component instead of Avatar

Summary: Now that we have UserAvatar we should render that for user avatars instead of Avatar

Test Plan: Tested that all user avatars are still able to be rendered correctly

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7259