[C++] Support duration type in floor_temporal/etc

[rok]

Describe the enhancement requested

The temporal rounding kernels round_temporal, floor_temporal, and ceil_temporal are currently only registered for date32/64, time32/64, and timestamp inputs (WithDates, WithTimes, WithTimestamps in scalar_temporal_unary.cc).

It would be useful to round duration inputs to multiples of physical and perhaps some calendar units.

Component(s)

C++