add on-visible-change event for modal show or hide/close

[renshuo]

add a event: on-visible-change
when visible of modal to be true or false, this event dispatched with new value of visible.

scene:
user open a modal with a form, one of the value in form should initialized by calling a REST service.
then user cancel or confirm the modal.
next, user reopen the modal, here need a new value by calling the REST service.

SO, add on-visible-change event for this scene.

[tangjinzhou]

Maybe you can use watch visible change to achieve this scene.

[Tianyz]

Maybe you can use watch visible change to achieve this scene.

But I think it would mess up my code, it's component's job to tell me when the visibility of Modal changed.
Just listen to open or close then run callbacks is better than write a watch and then check if visible true or false everywhere.
The proper way is both support the open and close event.

[github-actions]

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