[native] Introduce naive ChatThreadListSearch component

Summary:
This diff starts moving things from ChatThreadList to ChatThreadListSearch in a pretty naive/cut-and-paste way. Breaking into steps so I can make sure that things continue to work as expected after each change. Originally made all the changes at once and ran into weird issues I couldn't troubleshoot, so hopefully doing this incrementally will make it easier to narrow down.

This diff involves moving JUST the Search component to ChatThreadListSearch and ensuring that onChangeText, onBlur, and additionalProps get passed in and work as expected.

Test Plan: Search experience continues to work as expected.

Reviewers: ginsu, rohan, tomek

Reviewed By: ginsu

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D9205