Programatically show Cascader popup with popupVisible

[jhchill666]

What problem does this feature solve?

Currently, if using custom children in Cascader, for example to perform search using an async api, there is no way to display results in the popup. In the DropDown component, there is visible and onVisibleChange, to optionally make the component controlled.

In the render method of Cascader.js,, inputProps is composed of otherProps with certain props omitted. These include popupVisible. Would be simple enough to remove popupVisible from the omit, enabling the component to be 'controlled' fully.

Is there a valid reason, why this could not be supported?

What does the proposed API look like?

const inputProps = omit(otherProps, [
      'onChange',
      'options',
      'popupPlacement',
      'transitionName',
      'displayRender',
      'onPopupVisibleChange',
      'changeOnSelect',
      'expandTrigger',
      // 'popupVisible',
      'getPopupContainer',
      'loadData',
      'popupClassName',
      'filterOption',
      'renderFilteredOption',
      'sortFilteredOption',
      'notFoundContent',
    ]);