Issue #2248297 by Berdir: Fixed Ensure routes are rebuilt when install modules.

core/core.services.yml

core/lib/Drupal/Core/Config/ConfigImporter.php

core/lib/Drupal/Core/Extension/ModuleHandler.php

core/lib/Drupal/Core/Form/FormBuilder.php

core/modules/config/src/Form/ConfigSync.php

core/modules/system/src/Form/ModulesListConfirmForm.php

core/modules/system/src/Form/ModulesListForm.php

core/modules/system/src/Tests/Routing/RouterTest.php

core/modules/system/src/Tests/System/ThemeTest.php

core/tests/Drupal/Tests/Core/Form/FormTestBase.php