Disable use of method handle for core reflection in JDK21 and above

In JEP 416, core reflection was re-implemented with Method Handles with the
purpose of simplifying adding new language features. While analyzing
performance of workload based on large enterprise based application, I observed
that this was causing visible performance degradation. Disabling the use of
direct method handles for reflection calls while we are working on improving
the performance with direct method handles.

Signed-off-by: Rahil Shah <rahil@ca.ibm.com>

jcl/src/java.base/share/classes/java/lang/System.java

@@ -749,6 +749,12 @@ private static void ensureProperties(boolean isInitialization) {
 	initializedProperties.put("native.encoding", platformEncoding); //$NON-NLS-1$
 	/*[ENDIF] JAVA_SPEC_VERSION >= 17 */
 
+	/*[IF JAVA_SPEC_VERSION == 21]*/
+	if (null == initializedProperties.get("jdk.reflect.useDirectMethodHandle")) {
+		initializedProperties.put("jdk.reflect.useDirectMethodHandle", "false");
+	}
+	/*[ENDIF] JAVA_SPEC_VERSION == 21 */
+
 	/*[IF (JAVA_SPEC_VERSION >= 21) & (PLATFORM-mz31 | PLATFORM-mz64)]*/
 	initializedProperties.put("com.ibm.autocvt", zOSAutoConvert); //$NON-NLS-1$
 	/*[ENDIF] (JAVA_SPEC_VERSION >= 21) & (PLATFORM-mz31 | PLATFORM-mz64) */