Programmatic opening of date-picker component

[thinkdj]

What problem does this feature solve?

Sometimes, we need to open a DatePicker component without the user having to click on it. Proposing .open()/.close() methods. Problem with using existing option [nzOpen] is that the control of open/close completely becomes an onus on the programmer.

What does the proposed API look like?

datepickerTemplateRefVar.open(); & datepickerTemplateRefVar.close();