[lib] introduced reaction message spec boilerplate

Summary:
For this reaction message spec boilerplate, I implemented all of the required methods that a message spec requires. This includes the following functions: 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

As I continue to build out this reaction message spec and implement the other parts of message liking, I might be making some changes to these four functions especially as my understanding improves

Will be adding the other necessary functions for this message spec in subsequent diffs

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Depends on D5689
Linear Task: ENG-2245

Test Plan: Ran web and mobile app locally and nothing crashes/will be doing more tests on this message spec in subsequent diffs

Reviewers: atul, rohan, tomek

Reviewed By: atul, tomek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5690