[#257] Set the default validatedBy on the Constraint annotation

as part of: Support ConstraintValidator declaration via service loader [BVAL-645]

since there are different ways a constraint validator can be registered, there is no need to require an array of validators on constraint annotation...

Author: marko-bekhta

src/main/java/jakarta/validation/Constraint.java

@@ -87,5 +87,5 @@
 	 *
 	 * @return array of {@code ConstraintValidator} classes implementing the constraint
 	 */
-	Class<? extends ConstraintValidator<?, ?>>[] validatedBy();
+	Class<? extends ConstraintValidator<?, ?>>[] validatedBy() default {};
 }