As mentioned in [[
https://linear.app/comm/issue/ENG-3924/pinned-messages-not-showing |
ENG-3924 ]], there is an issue with some pinned messages where if they are
not present in Redux, they will not show up in the modal.
This is because `messageListData` will incorrectly set the messageInfo's
`isPinned` flag to false, and therefore we will filter it out. This diff
resolves this on `web` by keeping a Set of pinned messgae IDs, and
filtering out messages that are not part of the set, rather than based on
their `isPinned` value. This maintains the same behaviour for pinned
messages that were fetched, but also covers the case where they are not
part of Redux.