[web] Trigger sendCallbacks on multimedia messages

Summary:
This is part 2 of my comment on D7388:

Part of the issue is that sendCallbacks were only getting triggered for text messages on web. I believe this was an oversight... it is triggered for media on native, and it needs to be triggered for media on web as well in order for the "search" to be closed when a thread is created with a media message. This will be addressed in the next diff.

Depends on D7388

Test Plan: Create a thread by sending a media message on web and confirm that the "serach" experienced closes (it didn't before this diff)

Reviewers: tomek, inka

Reviewed By: tomek

Subscribers: atul

Differential Revision: https://phab.comm.dev/D7407