[native] move selectFromGalleryAndUpdateThreadAvatar to edit thread avatar provider

Summary: This diff breaks down D7643. This diff is simply now a move diff with one very minor change and is something I will annotate in the code below

Test Plan: I am able to set a thread image avatar with the expected behavior

Reviewers: atul, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7684