**Won't land this diff until all diffs for message spec are done**
For this reaction message spec boilerplate, I implemented all of the required methods that a message spec needs. This included: `messageTitle`, `rawMessageInfoFromClientDB`, `createMessageInfo` and `generatesNotifs`. I also added `messageContentForClientDB` because this goes hand in hand with `rawMessageInfoFromClientDB`.
For `rawMessageInfoFromClientDB`, I return the `targetMessageID` and the `reaction` and these will be in the content of `rawMessageInfoFromClientDB`.
For `messageTitle` I validate the message info and then call and return the results of `messagePreviewText` which was modified in D5689
For `rawMessageInfoFromClientDB` I am returning an object of all the necessary info I get from `clientDBMessageInfo`. This includes getting `targetMessageID` and `reaction` which I get from `content`.
For `createMessageInfo` I am grabbing the necessary information from `rawMessageInfo` and `creator` and returning a `ReactionMessageInfo` object
Will be adding the other necessary functions for this message spec in subsequent diffs
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Depends on D5689
Linear Task: [[ https://linear.app/comm/issue/ENG-2245/setup-message-reaction-spec | ENG-2245 ]]