[native] Lift FlatList to ConnectedChatThreadList

Summary:
This diff is just one step in the process of converting ChatThreadList into a functional component. When this work is done, we will be able to avoid a lot of re-rendering and hopefully improve performance quite a bit.

This should be the second to last diff in converting ChatThreadList to a functional component. After that I'll do some cleanup/refactoring to make the component more readable (group hooks, break search into its own component, etc).

Depends on D9183

Test Plan: ChatThreadList + search experience continue to work as expected.

Reviewers: ginsu, tomek, rohan

Reviewed By: ginsu

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9184