8297784: Optimize @stable field for Method.isCallerSensitive

Reviewed-by: redestad, jvernee, alanb

src/java.base/share/classes/java/lang/reflect/Method.java

@@ -605,13 +605,17 @@ private Object invoke(Object obj, Object[] args, Class<?> caller)
         return callerSensitive ? ma.invoke(obj, args, caller) : ma.invoke(obj, args);
     }
 
-    @Stable private Boolean callerSensitive;       // lazily initialize
+    //  0 = not initialized (@Stable contract)
+    //  1 = initialized, CS
+    // -1 = initialized, not CS
+    @Stable private byte callerSensitive;
+
     private boolean isCallerSensitive() {
-        Boolean cs = callerSensitive;
-        if (cs == null) {
-            callerSensitive = cs = Reflection.isCallerSensitive(this);
+        byte cs = callerSensitive;
+        if (cs == 0) {
+            callerSensitive = cs = (byte)(Reflection.isCallerSensitive(this) ? 1 : -1);
         }
-        return cs;
+        return (cs > 0);
     }
 
     /**