[native] change type for useProcessSelectedMedia from MediaLibrarySelection to NativeMediaSelection

Summary: we need to do this so we can extend useProcessSelectedMedia to handle images from camera capture in addition to images from photo gallery selection

Test Plan: flow

Reviewers: atul, ashoat

Reviewed By: ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7548