Date range selector should enforce end date > start date

Steps to repro:

1. Add a ui.input_date_range component
2. Select a start date
3. Select an end date < start date.  This is allowed.

Expected: Minimum selectable date for the end of the range should be the selected date for the start of the range.  This is consistent with standard UI practice.

Selecting a new start date > end date could reset the end date to the new start date.