[web] Keyboard support for typeahead [9/13] - Refactor getTypeaheadTooltipButtons as a function

Summary: Moved creating buttons in overlay to utility function.

Test Plan:
Typeahead without keyboard support works.
Final tests performed in last diffs.

Reviewers: inka, kamil, ginsu, tomek

Reviewed By: inka, tomek

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

Differential Revision: https://phab.comm.dev/D6049