Unable to use xsd:date/xsd:dateTime field in forms

[kburger]

Using server v1.17.2 and client v1.17.0. When using a shape that deals with dates or time, the client seems to break down. I've tested in FireFox and Safari, using this example shape:

[ sh:path dcterms:issued ;
  sh:datatype xsd:dateTime ; # or xsd:date
  sh:minCount 1 ;
  dash:viewer dash:LiteralViewer ;
  dash:editor dash:DateTimePickerEditor ; # or dash:DatePickerEditor
]

When creating new metadata with this shape, the form fails with the following error hint on the input field:
http://www.w3.org/ns/shacl#DatatypeConstraintComponent

We see the value in the form widget as expected, e.g. 2024-06-04 for a xsd:date/dash:DatePickerEditor or 2024-06-04 12:00 for a xsd:dateTime/dash:DateTimePickerEditor. In the RDF preview however, the value being used is always in the format of "Tue Jun 04 2024 00:00:00 GMT+0200 (Central European Summer Time)".

This formatted value will fail on SHACL validation, which expects an ISO8601 formatted date for xsd:date or timestamp for xsd:dateTime.

We believe this is a more generic description of the issue raised in #147.