Deprecate Connection::getDriverClass mechanism, make its callers abstract, and use standard autoloading

Problem/Motivation

As noted in #3186934: Introduce an ExceptionHandler class in the database API, deprecate Connection::handleQueryException, the way query classes are loaded by Connection is preventing static code analysis, besides being 'a magic' in the sense that they're autoloaded by placing files that override the base classes in the same directory where the Connection class resides.

Proposed resolution

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet