[native] Add some memoization to ChatThreadListSidebar

Summary:
Based on profiling flamegraph, it takes ~11ms to re-render ChatThreadListSidebar. If we have 4 ChatThreadListSidebars in the component tree re-rendering 5-6 times (as in "going to thread w/ varun scenario) that's ~220-264ms.

Depends on D9071

Test Plan:
Before:

After:

Reviewers: ginsu, rohan, tomek

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9072