For any given thread, we need to allow participants to view the pinned messages. The query checks for messages where `m.pinned = 1` and translates the rows into messageInfos using an existing
function. I use `shimUnsupportedRawMessageInfos` to prevent problems if there is a pinned message of a newer message type that an older client does not yet support.
Depends on D6930
Linear: https://linear.app/comm/issue/ENG-3186/add-a-fetchpinnedmessages-method-to-retrieve-all-pinned-messages-for-a