Fix #881 rounded date to string w/o UTC offset

Previously there was no combination of methods that would generate a
rounded AbsoluteDate without UTC offset, which was the behavior of
AbsoluteDate.toString() in Orekit 10. Added methods and tests.
2 jobs for legacy-to-string in 26 minutes and 28 seconds (queued for 1 second)
Status Name Job ID Coverage
  Verify
passed verify #3494

00:25:59

 
  Visualize
passed coverage-import #3495

00:00:28

97.0%