run-tests.sh - introduce an in-memory storage to replace --sqlite

Problem/Motivation

Right now, we are using --sqlite :memory: to store test results in throwaway CI environments.

In the past, the --sqlite option was necessary to pass data between different sub-processes, but since #3515347: Reduce run-tests.sh complexity in spawning subprocesses all data is available to the master process so it's no longer necessary persisting it, hence we started using :memory: for the SQLite test runner database. Right now, not specifying --sqlite means test results are stored to the installed Drupal database (remnant of simpletest times, when a testing UI was provided for test reporting).

Proposed resolution

Make so that if no --sqlite option is passed, test results are stored in an in-memory alternative implementation of TestRunResultsStorageInterface. This is dropping dependency from SQLite and avoid db roundtrips on behalf of an all-PHP implementation.

Introduce a --results-on-installed-db CLI option, alternative to --sqlite, that can be used to store results in the installed db (which is something that was discouraged time ago, anyway).

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet