[C++] Temporal floor/ceil/round throws exception for timestamps ambiguous due to DST

Running pyarrow.compute.floor_temporal for timestamps that exist will throw exceptions if the times are ambiguous during the daylight savings time transitions. 

As the \*_temporal functions do not fundamentally change the times, it does not make sense that they would fail due to a timezone issue. If they must fail, it should be when the pyarrow.Timestamp is created.

 

 
```java

import pyarrow
import pyarrow.compute as pc
import datetime
import pytz

t = pyarrow.timestamp('s', tz='America/New_York')

dt = datetime.datetime(2013, 11, 3, 1, 3, 14, tzinfo = pytz.timezone('America/New_York'))

# if a timestamp must be invalid, this could fail
za = pyarrow.array([dt], t)

# raises an exception, even though this is conceptually an identity function here
pc.floor_temporal(za, unit = 'second')
```
 

And this actually works just fine (continued from above)
```java

pc.cast(   
pc.floor_temporal(       
pc.cast(za, pyarrow.timestamp('s', 'UTC')),        
unit='second'),    
pyarrow.timestamp('s','America/New_York')
)

```
 

 

 

 

**Reporter**: [Kevin Crouse](https://issues.apache.org/jira/browse/ARROW-16022)
**Watchers**: [Rok Mihevc](https://issues.apache.org/jira/browse/ARROW-16022) / @rok

_{**Note**: *This issue was originally created as [ARROW-16022](https://issues.apache.org/jira/browse/ARROW-16022). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Start by reproducing the Python example with pyarrow.compute.floor_temporal on the America/New_York timestamp during the DST transition, then compare it with the UTC cast path shown in the issue. Trace the temporal floor, ceil, and round implementation and its timezone validation; done means ambiguous-but-existing timestamps no longer fail for these operations, with regression coverage for the reported case.

Written by the indexing model from the issue text.