created automatic_updates_test-api and refactored

...s_test_api/automatic_updates_extensions_test_api.info.yml

...dates_extensions/tests/src/Functional/UpdaterFormTest.php

...atic_updates_test_api/automatic_updates_test_api.info.yml

...c_updates_test_api/automatic_updates_test_api.routing.yml

.../modules/automatic_updates_test_api/src/ApiController.php

tests/src/Build/CoreUpdateTest.php

tests/src/Build/UpdateTestBase.php

tests/src/Functional/AutomaticUpdatesFunctionalTestBase.php

tests/src/Functional/UpdaterFormTest.php