Next to each pinned message, we want to display a pin icon to indicate that the message is pinned. We only want to show this icon in chat, and not the pin modal / pinned messages screen.

Logic is pretty much identical to https://phab.comm.dev/D7505

Depends on D7735

Linear: https://linear.app/comm/issue/ENG-3455/show-a-pin-icon-next-to-pinned-messages

Test to confirm that the pin indicator appears in chat and not the other instances where Message is rendered (like the pin modal and screen).

For iOS, the confirmation is that there are no message height inconsistencies in the terminal. For Android, they appear on master, but the message height warnings don't show for all of the pinned messages so it makes me believe no changes made in this diff cause the warnings.