#3599000 Date/time submission
Parse and validate date, datelist and datetime submissions (single and multiple value) through the submitWebform mutation, and strip the check-all/none sentinel on checkboxes submissions.
- WebformSubmit: wire date-family and Checkboxes plugins into form-state input so DateBase::validateDate() and Checkboxes::validateCheckAllOrNone() fire; strip disabled DateBase values; normalize multi-row and duplicated date error keys.
- Tests: FormSubmissionDatelistTest, FormSubmissionMultiDatetimeTest, FormSubmissionDateFamilyValidationTest and FormSubmissionCheckAllNoneTest; six date fixture elements; cascade row updates to the date read tests. Date tests assert timezone-derived values (no UTC pin) so they exercise the non-UTC timezone the test runner uses.
Closes #3599000