Reselect element with focus when datepicker closes

This is request for change.

When:

• user selects a value in datepicker
• user dismisses datepicker clicking outside or using ESC key
  previously select element should be probably reselected, as it’s done for modal with element to focus:
  https://github.com/ng-bootstrap/ng-bootstrap/blob/master/src/modal/modal-window.ts#L68

This would allow users to quickly reselect value in the case of e.g. minor error that could be quickly corrected
.
Other reference implementation supporting this behaviour:
https://material.angular.io/components/datepicker/overview
https://clarity.design/documentation/datepicker#examples

This would be non breaking change (unless some tests rely on keyboard navigation with presumed current focus behaviour).

Thanks!

NgBootstrap: 5.1