Issue #3420994 by kim.pepper: Convert RestResource plugin discovery to attributes

.../modules/dblog/src/Plugin/rest/resource/DbLogResource.php

...ules/file/src/Plugin/rest/resource/FileUploadResource.php

core/modules/rest/src/Attribute/RestResource.php

core/modules/rest/src/Plugin/Type/ResourcePluginManager.php

.../modules/rest/src/Plugin/rest/resource/EntityResource.php

...Plugin/rest/resource/NoSerializationClassTestResource.php

...ser/src/Plugin/rest/resource/UserRegistrationResource.php