Issue #3420988 by godotislate, smustgrave: Convert QueueWorker plugin discovery to attributes

core/lib/Drupal/Core/Queue/Attribute/QueueWorker.php

core/lib/Drupal/Core/Queue/QueueWorkerManager.php

...dules/locale/src/Plugin/QueueWorker/LocaleTranslation.php

...ules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php

...lugin/QueueWorker/CronQueueTestDatabaseDelayException.php

...test/src/Plugin/QueueWorker/CronQueueTestDeriverQueue.php

...ue_test/src/Plugin/QueueWorker/CronQueueTestException.php

...ue_test/src/Plugin/QueueWorker/CronQueueTestLeaseTime.php

.../Plugin/QueueWorker/CronQueueTestMemoryDelayException.php

.../src/Plugin/QueueWorker/CronQueueTestRequeueException.php

...test/src/Plugin/QueueWorker/CronQueueTestSuspendQueue.php