[Chapel Merge] Add operator '-' overload for datetime and date

Branch: refs/heads/master
Revision: 4292342
Author: daviditen
Log Message:

Merge pull request #17443 from king-11/operators

Add operator '-' overload for datetime and date

[PR by @king-11 reviewed and merged by @daviditen]

Modified Files:
M modules/standard/DateTime.chpl

Compare: https://github.com/chapel-lang/chapel/compare/94b89f8dd4f4...429234274328