Reset selection view to empty when no tabs are contributed
Currently the Simantics selection view as implemented by the org.simantics.selectionview
plugin keeps presenting the property view for an earlier but non-current selection until some other selection with non-empty contribution from a SelectionProcessor
is provided.
This may result in the selection view presenting a property editor for an obsolete resource or a resource that is out of current editor context until some other selection with editable properties is made. To allow editors to hide obsolete property editors from the selection view, the view needs to acknowledge an empty set of contributions from selection processors and show an empty view when no selection with editable properties is available.