fix: avoid "leaking" experimental features to stable interfaces (#22939)

* Avoid "leaking" experimental features to stable interfaces

Note, might be still binary incompatible, but at least shouldn't for users to implement this yet.

* Also add default impl for Classlist

Author: mstahv

flow-server/src/main/java/com/vaadin/flow/dom/ClassList.java

@@ -75,6 +75,9 @@ default boolean set(String className, boolean set) {
      *             thrown when there is already an existing binding
      * @since 25.0
      */
-    void bind(String name, Signal<Boolean> signal);
+    default void bind(String name, Signal<Boolean> signal) {
+        // experimental API, do not force implementation
+        throw new UnsupportedOperationException();
+    };
 
 }

flow-server/src/main/java/com/vaadin/flow/dom/Style.java

@@ -233,7 +233,10 @@ public interface Style extends Serializable {
      *
      * @since 25.0
      */
-    Style bind(String name, Signal<String> signal);
+    default Style bind(String name, Signal<String> signal) {
+        // experimental API, do not force implementation
+        throw new UnsupportedOperationException();
+    };
 
     /**
      * Sets the <code>background</code> property.