Added utility method Binder#asRequired() (#9873)

* Added the possiblity of defining a Field as Required without
setting an error message.

* Added @since to asRequired()

* Add droped paragraphs and see tag for asRequired(String)

server/src/main/java/com/vaadin/data/Binder.java

@@ -619,6 +619,31 @@ public class Binder<BEAN> implements Serializable {
             return asRequired(context -> errorMessage);
         }
 
+        /**
+         * Sets the field to be required. This means two things:
+         * <ol>
+         * <li>the required indicator will be displayed for this field</li>
+         * <li>the field value is validated for not being empty, i.e. that the
+         * field's value is not equal to what {@link HasValue#getEmptyValue()}
+         * returns</li>
+         * </ol>
+         * <p>
+         * For setting an error message, use {@link #asRequired(String)}.
+         * <p>
+         * For localizing the error message, use
+         * {@link #asRequired(ErrorMessageProvider)}.
+         *
+         * @see #asRequired(String)
+         * @see #asRequired(ErrorMessageProvider)
+         * @see HasValue#setRequiredIndicatorVisible(boolean)
+         * @see HasValue#isEmpty()
+         * @return this binding, for chaining
+         * @since 8.2
+         */
+        public default BindingBuilder<BEAN, TARGET> asRequired() {
+            return asRequired(context -> "");
+        }
+
         /**
          * Sets the field to be required. This means two things:
          * <ol>