In the last diff, I introduced a generic setUserAvatar in EditUserAvatarProvider. In a later diff, I'll add some logic that allows me to "override" the action that gets performed for a successful avatar selection, so that I can reuse it in the registration flow.

This code replaces useSaveUserAvatar with the generic utility, to make the codebase more consistent.

Depends on D8017

Test setting emoji avatar for user from iOS simulator