[TASK] Implement Value::getArrayRepresentation()

[oliverklee]

This implementation might get removed if all subclasses have their own implementation without needing the parent class implementation.

Part of #1440.

[coveralls]

coverage: 71.315% (-0.01%) from 71.329%
when pulling 7121481 on task/array-rep/value
into 6455dd1 on main.

[JakeQZ]

Descendent classes could call this parent method and merge the array, so they don't have make the getShortClassName() call themselves. Though the current implementations are, of course, not doing that (yet).

I wondered whether this would lead to an incomplete implementation in descendent classes where the method has not yet been implemented, but

• I don't think that matters;
• All descendent classes I checked have their own stub method throwing an exception, or an actual implementation.

This is a somewhat redundant change at the moment, until any descendent classes use parent::getArrayRepresentation(), but is nonetheless good for completeness.