[native] Added message editing

Summary: After pressing send button in edit mode, the message will be edited with new content.

Test Plan:
Tested on iOS, in edit mode:

• modified the content, pressed the sent button (the message has been edited, exited edit mode, restored draft),
• modified the content, pressed the sent button with disabled keyserver (an alert appeared, remained in edit mode):

• left the content the same, pressed the sent button (exited edit mode without alert, restored the draft).

Reviewers: michal, inka, ginsu

Reviewed By: inka

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7445