Fixed 'transaction named mimic_implicit_commit already in use' exception for...
https://www.drupal.org/project/drupal/issues/2920527
Fixed Postgres driver issue with nested savepoints mimic_implicit_commit
duplicated:
Initial work contributed by @jakegibs617 at: https://www.drupal.org/project/drupal/issues/2920527#comment-15412378
Added fix for queryTableInformation
based on work produced in intial patch.