Refactor: move disposing properties into the base class (#33740)

Moves more functionality to `base-component`, transferring the responsibility of disposal to parent class.
Each component, dusting disposal, sets its protected properties to `null`. So the same can be done in one place for all children components .

js/src/modal.js

@@ -183,6 +183,7 @@ class Modal extends BaseComponent {
     [window, this._dialog]
       .forEach(htmlElement => EventHandler.off(htmlElement, EVENT_KEY))
 
+    this._backdrop.dispose()
     super.dispose()
 
     /**
@@ -191,14 +192,6 @@ class Modal extends BaseComponent {
      * It will remove `EVENT_CLICK_DATA_API` event that should remain
      */
     EventHandler.off(document, EVENT_FOCUSIN)
-
-    this._config = null
-    this._dialog = null
-    this._backdrop.dispose()
-    this._backdrop = null
-    this._isShown = null
-    this._ignoreBackdropClick = null
-    this._isTransitioning = null
   }
 
   handleUpdate() {