Add the support for header in nodes (TOP_CENTER only)

[gcoutable]

A header can prevent child nodes from overlapping the label area. The header can be located at the top for TOP_XXX labels, the bottom for BOTTOM_XXX labels, on the left for LEFT_CENTER, and on the right for RIGHT_CENTER labels.

A CENTER label cannot have the property header -> This should not be possible in the creation of the InsideLabel#build() and we should thus throw an IllegalArgumentException here to prevent this use case from ever reaching the frontend. Add the class to a whitelist for the GeneralPurposeTests class. In the view DSL, always remove the header option, when converting, even if the option is true when the label's location is CENTER.

The label must be a header in a node with a list layout strategy. Throw an exception if that's not the case. In the view DSL, always set the header option to true if the parent node has a list layout strategy even if the option is set to false.

org.eclipse.sirius.components.diagrams.RectangularNodeStyle#withHeader should move to InsideLabelDescription.