[web] introduce useReactionTooltip hook

Summary:
This hooks runs all the logic necessary to create the reaction tooltip, and returns the onMouseEnter and onMouseLeave callbacks to be forwarded to the ReactionPill

Linear task: https://linear.app/comm/issue/ENG-3105/introduce-a-new-pop-up-component-that-renders-everytime-a-users-mouse

Depends on D8857

Test Plan:
Please see the demo video below

above:

below (not the default position, but just changed it for testing purposes):

Reviewers: atul, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8859