Use GlobalDBSingleton when touching database from the native iOS code.

Summary: This differential replaces any direct database access in iOS native code with GlobalDBSingleton API

Test Plan: Creating test release with those changes would remove iOS 137 crash

Reviewers: tomek, atul, jon

Reviewed By: tomek, jon

Subscribers: ashoat, abosh

Differential Revision: https://phab.comm.dev/D5234