[web] Keyboard support for typeahead [12/13] - Scrolling thourgh overlay as user interacts with it

Summary: Overlay scrolls automatically when users moves through users suggested to mention.

Test Plan:
Tested on video below:

Reviewers: inka, kamil, ginsu, tomek

Reviewed By: tomek

Subscribers: ashoat, atul, tomek, ginsu, kamil, inka

Differential Revision: https://phab.comm.dev/D6052