DB Backend: remove `basestore.NewWithDB`
Created by: camdencheek
This replaces the last instances of basestore.NewWithDB()
and removes the function. Instead of constructing stores from a dbutil.DB
interface, now we construct stores using other shareable handles or from transactable handles directly.
Depends on https://github.com/sourcegraph/sourcegraph/pull/36924 (sorry for the weird dependency. I had a couple of branches going. Will rebase once that's merged)
Test plan
Unit tests.