[native] Pull selectFromGallery/useUploadSelectedMedia out from EditUserAvatarProvider

Summary:
As part of making EditUserAvatarProvider "platform-agnostic" so it can be used across web and native, we're pulling selectFromGallery and useUploadSelectedMedia out of EditUserAvatarProvider.

Depends on D8213

Test Plan: Made sure I could still successfully select/upload image avatar from native.

Reviewers: ashoat, ginsu

Reviewed By: ginsu

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D8215