[native] Memoize SwipeableThread

Summary:
The real performance gains will come from adding memoization to ChatThreadListItem and ChatThreadListSidebar, but this is a prerequisite for those optimizations to make a difference.

Depends on D9099

Test Plan: Continue to look and behave as expected.

Reviewers: ginsu, rohan, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9100