[lib] Exclude users that don't support thick threads from results
Summary:
When a user can't be added to thick thread, they shouldn't be included in search results.
Depends on D13404
Test Plan: Checked that the user who don't support thick threads aren't shown in add member modals of thick threads.
Reviewers: kamil, will
Reviewed By: kamil
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D13405