The last step of ENG-4849 is to simplify the derived messages logic in fetchDerivedMessages. Ideally, rather than handling parsing out the JSON object in the function itself, we'll introduce a function in specific message specs (only SIDEBAR_SOURCE and TOGGLE_PIN since those are the ones that are involved here) that, if defined, contains the logic for parsing in itself. This once again moves the source of truth to the message specs. The next diff will involve updating the callsites of rawMessageInfoFromServerDBRow to only pass in derivedMessages as a param if this function is defined in the message spec.
Depends on D9538