Issue #3404429: Add getType to StageBase to allow subclasses to be internal

automatic_updates_extensions/src/ExtensionUpdateStage.php

...dates_extensions/src/Validator/UpdateReleaseValidator.php

package_manager/src/FailureMarker.php

package_manager/src/StageBase.php

...ts/modules/package_manager_test_api/src/ApiController.php

...ger/tests/src/Functional/FailureMarkerRequirementTest.php

...manager/tests/src/Kernel/PackageManagerKernelTestBase.php

package_manager/tests/src/Unit/StageBaseTest.php

src/ConsoleUpdateStage.php

src/MaintenanceModeAwareCommitter.php

src/UpdateStage.php

src/Validator/CronFrequencyValidator.php

src/Validator/PhpExtensionsValidator.php

src/Validator/StagedDatabaseUpdateValidator.php

src/Validator/VersionPolicyValidator.php

src/Validator/WindowsValidator.php

tests/src/Kernel/AutomaticUpdatesKernelTestBase.php