ui: add disabledconstrainToWindow to avoid filp

packages/ui-default/components/dropdown/Dropdown.js

@@ -30,7 +30,7 @@ export default class Dropdown extends DOMAttachedObject {
       content: this.options.target || $.find($dom.attr('data-dropdown-target'))[0],
       position: this.options.position,
       openOn: 'hover',
-      constrainToWindow: true,
+      constrainToWindow: $dom.attr('data-dropdown-disabledconstrainToWindow') === undefined,
       constrainToScrollParent: false,
     });
     this.dropInstance.on('open', this.onDropOpen.bind(this));