feat: add a feature flag for new field validation behavior (#14285)

This PR adds a feature flag for the new field validation behavior. The flag will be used by Flow field components. For more information about the new behavior, please refer to vaadin/platform#3066.

Part of vaadin/platform#3066

flow-server/src/main/java/com/vaadin/experimental/FeatureFlags.java

@@ -75,6 +75,10 @@ public class FeatureFlags implements Serializable {
             "Collaboration Engine backend for clustering support",
             "collaborationEngineBackend",
             "https://github.com/vaadin/platform/issues/1988", true, null);
+    public static final Feature ENFORCE_FIELD_VALIDATION = new Feature(
+            "Enforce client / constraint / binder validation",
+            "enforceFieldValidation",
+            "https://github.com/vaadin/platform/issues/3066", false, null);
     private List<Feature> features = new ArrayList<>();
 
     File propertiesFolder = null;
@@ -98,6 +102,7 @@ public FeatureFlags(Lookup lookup) {
         features.add(new Feature(OFFLINE_LICENSE_CHECKER));
         features.add(new Feature(COLLABORATION_ENGINE_BACKEND));
         features.add(new Feature(WEBPACK));
+        features.add(new Feature(ENFORCE_FIELD_VALIDATION));
         loadProperties();
     }