[lib] introduce notificationCollapseKey function to reaction message spec

Summary:
introduce notificationCollapseKey function to reaction message spec. For this method, I returned the joined result of the type, threadID, creatorID, and targetMessageID fields. By using these fields, a notification will be collapsed and won't alert the user if someone is quickly liking and then unliking the same message. I felt that this was reasonable, but can also see that we might want to remove targetMessageID from the joined results to make it less "spammy" if a user likes a bunch of messages in the same thread.

Depends on D5870
Linear Task: ENG-2245

Test Plan:
Please watch the demo video to see the changes I made

Reviewers: atul, tomek, rohan, ashoat

Reviewed By: tomek, ashoat

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5871