DMN12 — Missing attribute isExpanded for DecisionService DI

There is three ways to depict a decision service in DMN 1.2:
Expanded with the divider line
Expanded without the divider line.
Collapsed with the plus maker

However, in the lastest version of the specification (from Ballot 15) in the Decision Service section only 2 depictions are shown: the expanded one, with and without divider line.

To have the last one, we need to add an isExpanded attribute to DMNShape.

Add isCollapsed attribute to DMNShape

See revised text.