Issue #3502882 by catch, alexpott, godotislate: Add a classloader that can handle class moves

core/core.services.yml

core/includes/bootstrap.inc

...al/Core/ClassLoader/BackwardsCompatibilityClassLoader.php

core/lib/Drupal/Core/CoreServiceProvider.php

...ection/Compiler/BackwardsCompatibilityClassLoaderPass.php

core/lib/Drupal/Core/DrupalKernel.php

...es/module_autoload_test/module_autoload_test.services.yml

...ore/ClassLoader/BackwardsCompatibilityClassLoaderTest.php

...l/Tests/Core/StringTranslation/TranslationWrapperTest.php