Datepicker: Allow controlled clearing of input

[interactivellama]

Currently, on initial load the input is uncontrolled and creates a clear empty string value. There currently is not a way to reset to an empty string once the value is set.

One proposal is to allow a controlled component reset to input empty string by using value={null}.

[stale[bot]]

This issue has been automatically marked as stale, because it has not had recent activity. It will be closed if no further activity occurs. Maintainers are responsible for tech debt and project health. This is most likely a new components or component feature request. Please submit a pull request for or request feedback on this feature. Thank you.