Issue #2540416 by dawehner, hussainweb: Move update.php back to a front controller

core/lib/Drupal/Core/Update/UpdateKernel.php

core/modules/simpletest/src/AssertContentTrait.php

core/modules/system/src/Controller/DbUpdateController.php

...stem/src/Tests/Update/UpdatePathWithBrokenRoutingTest.php

core/modules/system/src/Tests/Update/UpdateScriptTest.php

core/modules/system/system.routing.yml

.../system/tests/fixtures/update/drupal-8.broken_routing.php

...ipt_test/src/PathProcessor/BrokenInboundPathProcessor.php

...odules/update_script_test/update_script_test.services.yml

update.php