feat(datepicker): When changing date, optionally keep selected time from connected time picker

[meblum]

Feature Description

Currently, when the time picker is integrated with a date picker and the date is changed, the time will reset to 0 (see demo).
Ideally there should be an option to keep the selected time when changing the date.

Use Case

It is confusing and tedious for the user to have them reenter the time just because they have chosen to change the date.

[crisbeto]

Note that this would likely be in the datepicker, not the timepicker.