Improve tests for primitives that use Datetime inputs

For most datetime primitives, improper conversion of a timezone aware datetime value to a different timezone or UTC could result in the primitives returning incorrect values. For example, converting a time in the US to UTC will result in a change in the hour of the datetime and could also result in a change in the Day, Month, Week, or Year, depending on the datetime values.

We need to be careful to avoid improper timezone conversions inside the primitive functions. We should add tests for all datetime primitives in which a conversion between timezones could result in an incorrect output to make sure we aren't inadvertently performing operations inside the primitives that cause incorrect results.