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