DiagramServices::getEditPart(DDiagramElement) can cause deadlock

[mPorhel]

In some situations, deadlock can occur during refresh of diagrams having the capability to display functional chains or physical paths: ie diagrams with Sirius post refresh extensions :

• org.polarsys.capella.core.sirius.analysis.refresh.extension.ComponentArchitectureBlankRefreshExtension.postRefresh(DDiagram)
• org.polarsys.capella.core.sirius.analysis.refresh.extension.DataFlowBlankRefreshExtension.postRefresh(DDiagram)
• org.polarsys.capella.core.sirius.analysis.refresh.extension.EntityArchitectureBlankRefreshExtension.postRefresh(DDiagram)

The detected performance issue or potential deadlock comes from the DiagramServices::getEditPart(DDiagramElement) which uses an helper using Display.syncExec method to get the ActiveEditor.
This also means that a refresh occuring on a non active editor will not refresh the edit parts.

Reproduction scenario exists with Team for Capella:

• when a user has received remote changes on a locked diagram, if the automatic refresh is disabled, this diagram will be frozen and will need a manual refresh to display the received remote changes and be refresh accordingly to potential local changes.
• with Capella 6.1 and 7.0 (an dI assume 5.2/6.0), with the [LAB] [Build] All Components, Functions, CEs, FEs diagram from the IFE sample, I get a ~29s manual refresh for this particular scenario compared to an immediate (200ms to 1s regarding the versions) time for other refresh use cases of the same diagram
• analysis targets the DiagramService::getEditPart implementation

[mPorhel]

With the provided PR, the issue is no more reproduced with the scenario we have with Team for Capella.
The particular refresh done on a frozen diagram comes back to the same timings than other refreshes.