Enhance DMActivityHandler

Summary: This differential addresses Ashoat review for this diff: https://phab.comm.dev/D13246

Test Plan:

1. Create thick thread between users A and B.
2. Log in as user A on two devices (on web and on native) and log in as user B on third device.
3. Send message from B to A. Open the thread as A on web. Ensure rescinding happens on native.
4. Open the thread as A on native. Change opened thread as A on web. Send messages from B to A. Ensure that thread remains read on web.

Reviewers: tomek, kamil, ashoat

Reviewed By: ashoat

Differential Revision: https://phab.comm.dev/D13305