[native] refactor migrate() method to static member of SQLiteQueryExecutor

Summary:
Motivation:

1. Migration process is not connected to query executor instance, but to database (specific one, SQLite in this case) in general.
2. In next diff from the stack we will need to make clearSensitiveData also static and we will not be able to use this->migrate() there.

Test Plan: Build the app and run migrations, there should behave the same way as previously

Reviewers: marcin, tomek

Reviewed By: marcin, tomek

Subscribers: ashoat, tomek, atul

Differential Revision: https://phab.comm.dev/D5988