[web] Close thread composer after sending a message

Summary: Register hideSearch callback to be executed after sending a message, so the chat creation view disappear when sending to the message.

Test Plan: After introducing chat creation view, sending any message into existing or pending thread in thread creation mode should close the thread composer panel.

Reviewers: tomek, atul, abosh

Reviewed By: tomek, atul

Subscribers: ashoat, adrian, abosh

Differential Revision: https://phab.comm.dev/D4464