[web] cleanup message reactions modal
Summary:
This diff cleans up the one off styles in the message reactions modal and replaces it with styles of the redesigned modal.
Linear task: Linear task: https://linear.app/comm/issue/ENG-5943/extendmodify-the-modal-props-api-to-follow-new-modal-designs
Depends on D10269
Test Plan:
Please see screenshot below
Reviewers: atul, rohan, kamil
Reviewed By: rohan
Subscribers: ashoat, tomek
Differential Revision: https://phab.comm.dev/D10273