[native] Move MessageStoreTransform to lib

Summary:
ENG-3490 : Migrate stores to SQLite on web
Now that we have will start persisting message store in sqlite on web, we need to have a redux transform, like on native which will split data between persited by redux and persisted by sqlite. This diff moves the transform to lib (+ updated comments). The transformer will be added to web in the later diffs.

Depends on D11536

Test Plan: Check if the app on native works. Check if rehydrated store contains data from both sources.

Reviewers: kamil, marcin

Reviewed By: kamil

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11537