[web] show which reactions the viewer has already selected in the inline engagement

Summary:
To improve the user experience of the inline engagement, we should show/indicate to the user which reactions they have already selected. We indicate this to the user by adding a border to the reaction pill.

Depends on D8808

Test Plan:
Confirmed the width/height of the reaction pills are all the same regardless if it has been selected by the viewer or not

Please watch the demo video below:

Reviewers: atul, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8810