refactor: override global contextmenu handler in submenu

Recent listener-lifecycle refactor moved the global "contextmenu"
binding out of `_openedChanged`, so submenu must override
`__onGlobalContextMenu` directly to ignore those events. Drop the
now-redundant `__restoreOpened` reset in `connectedCallback` since the
flag is recomputed on each disconnect.

Author: vursen

packages/context-menu/src/vaadin-context-menu-mixin.js

@@ -150,7 +150,6 @@ export const ContextMenuMixin = (superClass) =>
       // Restore opened state if overlay was opened when disconnecting
       if (this.__restoreOpened) {
         this._setOpened(true);
-        this.__restoreOpened = false;
       }
     }
 

packages/menu-bar/src/vaadin-menu-bar-submenu.js

@@ -102,13 +102,21 @@ class MenuBarSubmenu extends ContextMenuMixin(ThemePropertyMixin(PolylitMixin(Li
   }
 
   /**
-   * Overriding the observer to not add global "contextmenu" listener.
+   * Overriding the observer to not toggle user-select on the host.
    * @override
    */
   _openedChanged() {
     // Do nothing
   }
 
+  /**
+   * Overriding the handler to not react to global "contextmenu" events.
+   * @override
+   */
+  __onGlobalContextMenu() {
+    // Do nothing
+  }
+
   /**
    * Overriding the public method to reset expanded button state.
    */