[native] have actionsheet pop up on press when editing avatar

Summary:
When the user now presses on a user or thread avatar in the profile or thread settings, an action sheet popups displaying various options for editing an avatar. For this diff the only option is the emoji avatar edit flow; however, diffs further down this stack will introduce other edit options

Test Plan:
Please watch the demo videos:

iOS:

Android:

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7459