Sets or gets the value of the date picker.
Setting the value property sets the date displayed in the date picker element.
Notes:
Changing a date picker's value in code doesn't trigger an onChange event.
If a date picker is connected to a dataset, setting the date picker's value
in code doesn't set the value of the connected field in the dataset.
That means if you use the dataset to perform a submit, the value changed
in code isn't reflected in the submitted item.
To submit the new value using a dataset, set the field's value using the
setFieldValue() function before
performing the submit.