[web] Displaying 'Edit' label next to edited messages

Summary: Added displaying 'Edit' label next to edited messages.

Test Plan:
Tested displaying on both sides (left and right) with:

1. message not edited and without thread/reactions,
2. message edited without thread/reactions,
3. message not edited with thread/reactions,
4. message edited with thread,
5. message edited with reactions,
6. message edited with thread and reactions,
7. many edited messages in a row,

Screenshots:
[1, 2, 3, 5, 6]

Reviewers: michal, inka, ginsu

Reviewed By: ginsu

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D7018