[web] introduce ReactionTooltip component

Summary:
This diff introduces the ReactionTooltip component that we be rendered whenever a user hovers over a reaction pill. This diff just introduces the component and subsequent diffs will handle the other parts to building a tooltip (calculating the tooltipSize and creating the hook that will create this tooltip)

Here is the linear thread where we discuss what should the ReactionTooltip look like

Here is the design (there are some changes and all of this was discussed in the linear thread):

Something to note about the tooltip is that see more will conditionally render based on if 6 or more users have reacted to that message with the same reaction

Depends on D8831

Test Plan:
Please see the demo video below to see what the tooltip looks and behaves like:

Reviewers: atul, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8823