The goal here is to allow using Doctrine for Field Types external storage, so in the future we can remove our own layer (identified as "legacy" storage engine).

Part 1: prepare kernel for new storage engine by injecting Doctrine object instead of “legacy" layer to Field Type external data, so Field Types get access to both “legacy” and Doctrine.

Part 2: refactor a few Field Types to use Doctrine instead (+ aim to optimize external storage DB code).