[native] Show ActivityIndicator in EditUserAvatar during update

Summary:
We consume isGalleryAvatarUpdateLoading and isRemoveAvatarUpdateLoading introduced in previous diffs to display ActivityIndicator (ie spinner) when an update is in progress.

Note: Yeah there are obvious things that can be factored out. I want to get more of the error handling stuff done first and then I'll go through and consolidate things.

Depends on D7528

Test Plan:
Works as expected:

Reviewers: ashoat, ginsu

Reviewed By: ashoat

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7529