In Sequence Diagram, improve ReorderTool to allow lifeline change

[peransin-obeo]

When drag-n-dropping node in Sequence Diagram, it is possible to change elements order but not elements lifeline even if gef/gmf provides indication to do so.

Usecase

See this demo video using org.eclipse.sirius.sample.interactions.design plugin

With proper variables about target node, developer would be able to change its model to move the execution into lifeline 'newParticipant1'.

Analysis

These are the step to introduce this feature:

• Add variables 'beforeContainerView' and 'afterContainerView' in tool property
• Evaluates such variables in
  

  sirius-desktop/plugins/org.eclipse.sirius.diagram.sequence/src/org/eclipse/sirius/diagram/sequence/business/internal/operation/SynchronizeISequenceEventsSemanticOrderingOperation.java

  Line 137 in 03aee7f

  private void updateSemanticPosition(ISequenceEvent eventToUpdate) {

• if values are different apply this sequence:
  

  sirius-desktop/plugins/org.eclipse.sirius.diagram.sequence/src/org/eclipse/sirius/diagram/sequence/business/internal/operation/SynchronizeISequenceEventsSemanticOrderingOperation.java

  Line 182 in 03aee7f

  applySemanticReordering(semanticElement, startingEndPredecessorAfter, finishingEndPredecessorAfter, reorderTool);

[mPorhel]

This evolution might be more complicated than just addition of the variables as indicated in previous comment.

Several modifications of the editpolicy / move validator / move command builder of the ExecutionEditPart will be needed to allow drag and drop to another lifeline and ensure a consistent layout.

In the VSM this might also lead to the use of a drop tool in combination with the reorder tool. The drop tool will handle the semantic part of the parent change.

Regarding layout and command modifications, they might be in the same area than the changes done for #536 .