[native] Extract default Redux state to separate file

Summary: I want to import it from persist.js, but that would introduce a circular dependency since redux-setup.js already imports persist.js. The solution is to extract it to a separate file.

Test Plan:

1. Flow
2. Confirmed that app starts correctly "from scratch" (no persisted Redux store)
3. Confirmed that app starts correctly from an existing Redux store

Reviewers: tomek, michal

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D9185