UML25 — Activity::structuredNode is incorrectly marked as readOnly = true

Activity::structuredNode is incorrectly marked as readOnly = true

This appears to be a throwback to 2.4, in which it was also marked as derived - it got marked as not derived
by the resolution to urgent issue 16232. In 2.4 it was readonly and derived; in 2.4.1 it was neither (which
means that readonly was removed when the issue was applied, even though the issue did not call for that);
in 2.5 it has for some reason become readonly again. The only explanation I might offer for this is that
somebody noticed while applying 16232 that readonly needed to be removed and did it, but this change did
not get checked in.
The resolution is to set readOnly to false. The only impact on the specification document is figure 16.45,
which needs to be changed. The generated classifier descriptions do not contain the

annotation

• this is a separate issue which will need to be addressed in the future but is too disruptive to address at
  the time of writing. The consequence is that no change is needed to the generated classifier description for
  Activity::structuredNode.