HHH-19639 Add EmbeddableFetchImpl#getNullIndicatorResult

In Hibernate Reactive, `ReactiveEmbeddableFetchImpl#createInitializers`
needs to access the value to override the initializer created by ORM.

Author: DavideD

hibernate-core/src/main/java/org/hibernate/sql/results/graph/embeddable/internal/EmbeddableFetchImpl.java

@@ -210,4 +210,9 @@ public FetchParent asFetchParent() {
 	protected BasicFetch<?> getDiscriminatorFetch() {
 		return discriminatorFetch;
 	}
+
+	// Used by Hibernate Reactive
+	protected @Nullable DomainResult<Boolean> getNullIndicatorResult() {
+		return nullIndicatorResult;
+	}
 }