[web] Keyboard support for typeahead [2/13] - Moved typeahead-utils.js

Summary: Moved utility functions to web/utils.

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

Reviewers: inka, kamil, ginsu, tomek

Reviewed By: ginsu, tomek

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

Differential Revision: https://phab.comm.dev/D6042