Issue #1846454 by chx, dawehner, amateescu: Add Entity query to Config entities.

core/includes/entity.inc

...lib/Drupal/Core/Config/Entity/ConfigStorageController.php

core/lib/Drupal/Core/Config/Entity/Query/Condition.php

core/lib/Drupal/Core/Config/Entity/Query/Query.php

core/lib/Drupal/Core/Config/Entity/Query/QueryFactory.php

core/lib/Drupal/Core/CoreBundle.php

core/lib/Drupal/Core/Entity/Query/QueryFactory.php

...Drupal/config_test/Plugin/Core/Entity/ConfigQueryTest.php

...sql_storage/lib/Drupal/field_sql_storage/Entity/Query.php

.../lib/Drupal/system/Tests/Entity/ConfigEntityQueryTest.php