[native] clean up InlineEngagement component

Summary:
Small cleanup diff to better organize and make the InlineEngagement component easier to read/go through. The two changes to note are

1. Renamed threadInfo to sidebarInfo: I thought that this was a more accurate name since this was holding the sidebar thread info
2. Reorganized/moved the styles unboundStyles so that the order of the styles went from usage in parent elements/containers to the children elements. Before this the styles were in some random order that didn't make any sense to me

Depends on D8317

Test Plan: Confirmed that InlineEngagment still looked and behaved the same.

Reviewers: atul, kamil

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D8496