[lib] Introduce basic unit tests for ThreadOpsUtils

Summary:
Depends on D7300

Mostly a sanity test that convertRawThreadInfoToClientDBThreadInfo and convertClientDBThreadInfoToRawThreadInfo are inverse functions with/without avatar field included.

Test Plan: yarn test and they succeed

Reviewers: ashoat, ginsu

Reviewed By: ginsu

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7303