[lib] Handle pinnedCount in convertClientDBThreadInfoToRawThreadInfo

Summary:
Even after persist.js migration 36 it looked like the threadInfos stored on the client were missing the pinnedCount field.

After taking a look at CommCoreModule it seemed like everything was good. However, noticed that convertClientDBThreadInfoToRawThreadInfo was missing pinnedCount entirely. This means that RawThreadInfos we get from SQLite will ALWAYS have pinnedCount stripped out even if it is properly persisted in SQLite.

Test Plan: Ongoing... as a start will check SET_CLIENT_DB_STORE action in Redux Dev Tools and see if ThreadInfos include pinnedCount field.

Reviewers: ashoat, rohan

Reviewed By: ashoat, rohan

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D7587