There is no way to disable the close button

[Ke1sy]

In our project we have the form inside the dialog and a potentially long-running API call that is made upon clicking the “ok” button and we need to prevent the user from closing the modal while the API call is still pending. Currently there is no way to disable close (X) button while the API is still in flight.
According to our design the modal should be closable, so I cannot use closable={false}.
I propose to add an additional prop closeBtnIsDisabled that will allow user to disable the close button.
Let me know if you accept such PR.

[Ke1sy]

@yoyo837 @zombieJ @MadCcc Let me know if you accept such PR in rc-dialog and later in antd. Thanks!