Change return type of UpdateDefinition.isIsolated to primitive.

Switch return from Boolean to boolean.

Closes: #4922
Original Pull Request: #4981

Signed-off-by: Hyunsang Han <gustkd3@gmail.com>

Author: HyunSangHan

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/MappedDocument.java

@@ -140,7 +140,7 @@ public void inc(String version) {
 		}
 
 		@Override
-		public Boolean isIsolated() {
+		public boolean isIsolated() {
 			return delegate.isIsolated();
 		}
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/aggregation/AggregationUpdate.java

@@ -248,7 +248,7 @@ public AggregationUpdate isolated() {
 	}
 
 	@Override
-	public Boolean isIsolated() {
+	public boolean isIsolated() {
 		return isolated;
 	}
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/query/Update.java

@@ -444,7 +444,7 @@ public Update filterArray(String identifier, Object expression) {
 	}
 
 	@Override
-	public Boolean isIsolated() {
+	public boolean isIsolated() {
 		return isolated;
 	}
 

spring-data-mongodb/src/main/java/org/springframework/data/mongodb/core/query/UpdateDefinition.java

@@ -24,6 +24,7 @@
  *
  * @author Christoph Strobl
  * @author Mark Paluch
+ * @author Hyunsang Han
  * @since 2.2
  */
 public interface UpdateDefinition {
@@ -34,7 +35,7 @@ public interface UpdateDefinition {
 	 *
 	 * @return {@literal true} if update isolated is set.
 	 */
-	Boolean isIsolated();
+	boolean isIsolated();
 
 	/**
 	 * @return the actual update in its native {@link Document} format. Never {@literal null}.