Refactor getAllDrafts. Bring db drafts parsing to separate function

Summary: This differential refactors getAllDrafts method so that draft parsing is implemented in separate function. This is going to be used when creating bulk JSI query for all SQLite data

Test Plan: Launch the app, write some drafts, kill the app. Launch the app, launch Flipper ensure SET_CLIENT_DB_STORE action payload has corract drafts property.

Reviewers: tomek, atul, jon

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D5771