DATACMNS-1508 - Polishing.

Add findAllById, deleteAll to CoroutineCrudRepository.

Keep CoroutineCrudRepository somewhat in sync with ReactiveCrudRepository by adding based methods for those accecpting Publisher.
Also add some test.

Update License Headers of Kotlin files and fix some warnings. Switch to kotlin-test-junit5.

Original pull request: #415.

src/test/java/org/springframework/data/repository/core/support/DummyRepositoryFactory.java

@@ -112,7 +112,7 @@ public class DummyRepositoryFactory extends RepositoryFactorySupport {
 	/**
 	 * @author Mark Paluch
 	 */
-	public static interface MyRepositoryQuery extends RepositoryQuery {
+	public interface MyRepositoryQuery extends RepositoryQuery {
 
 	}
 }