[native] Launch message editing on mobile

Summary: Doing this via feature flag service carries the risk that the request times out. Until that problem is solved, figure it's safer to launch via code change.

Test Plan: Message editing has been tested by @kuba already. For this simple change, relying on Flow / ESLint

Reviewers: kuba, atul

Reviewed By: atul

Subscribers: tomek, kuba

Differential Revision: https://phab.comm.dev/D8005