[lib, native, web] move onChangeSearch to hook

Summary: move onChangeSearch to lib/hooks/ from native and web.

Test Plan: Use the search sidebar feature in both native and web and confirm functionality still works as expected.

Reviewers: atul, palys-swm, def-au1t

Reviewed By: atul

Subscribers: ashoat, Adrian, yayabosh

Differential Revision: https://phabricator.ashoat.com/D4057