Add warning if out events are checked in reactions but are not raised before.

[terfloth]

If out events are used as reaction triggers or in reaction guards but are not raised in the statechart then they will always evaluate to false. It makes sense to provide a hint to the user to explain the constraint and avoid confusion.

A validation rule with the following properties must be implemented.

• [ ] The validation rule creates a warning with the message "Out event is never raised in this statechart and thus is never active".
• [ ] Check out events that are used as trigger or part of the guard expression on transitions and local reactions.
• [ ] The condition is true if there is no raise statement for the out event in the whole statechart.

This issue was derived from issue #2205 .

[terfloth]

The objection that this ticket does not make sense as out events just can be raised but not handled is false.

The statechart can react on out events that were raised before. While this "feature" can generally be questioned it is not possible to change this for the current implementations as this can break existing customer models.