[web] Implement callbacks modifying navigation from ChatThreadComposer

Summary: Introduce implementation of functions modifying navigation state after adding/removing user to list of selected and after exiting thread creation mode.

Test Plan: The component is not used in app yet. Tested it by performing different sequences of operations on users after introducing chat creation view in next diffs.

Reviewers: tomek, atul, abosh

Reviewed By: tomek, atul

Subscribers: ashoat, adrian, abosh

Differential Revision: https://phab.comm.dev/D4462