docs: deprecate the iron-resize event [skip ci] (#2238)

Author: Viktor Lukashov

packages/vaadin-split-layout/src/vaadin-split-layout.js

@@ -348,6 +348,7 @@ class SplitLayoutElement extends ElementMixin(
    * Fired when the splitter is dragged. Non-bubbling. Fired for the splitter
    * element and any nested elements with `IronResizableBehavior`.
    *
+   * DEPRECATED: This event will be dropped in one of the future Vaadin versions. Use a ResizeObserver instead.
    * @event iron-resize
    */
 

packages/vaadin-text-field/src/vaadin-text-area.js

@@ -219,6 +219,7 @@ class TextAreaElement extends ElementMixin(TextFieldMixin(ControlStateMixin(Them
   /**
    * Fired when the text-area height changes.
    *
+   * DEPRECATED: This event will be dropped in one of the future Vaadin versions. Use a ResizeObserver instead.
    * @event iron-resize
    */
 }

packages/vaadin-text-field/src/vaadin-text-field-mixin.js

@@ -869,6 +869,7 @@ export const TextFieldMixin = (subclass) =>
     /**
      * Fired when the size of the element changes.
      *
+     * DEPRECATED: This event will be dropped in one of the future Vaadin versions. Use a ResizeObserver instead.
      * @event iron-resize
      */
   };