Transient layers are not activated when diagram is reopened

[peransin-obeo]

When opening an existing diagram for the first time after loading a session, transient layer is not activated.

This is not conform with documentation:
https://eclipse.dev/sirius/doc/specifier/diagrams/Diagrams.html#Transientlayer

The behavior occurs while executing:

sirius-desktop/plugins/org.eclipse.sirius.diagram.ui/src-diag/org/eclipse/sirius/diagram/ui/tools/internal/editor/DDiagramEditorImpl.java

Line 598 in 33b42e3

private void activateTransientLayers() {

The 'transientLayersToActivate' list contains the same layers twice.
As activation is performed by a toggling command, layer is activated the desactivated.

The simplest fix is to check the getInitialActiveLayers method does not provide the same layer twice by adding a containment verification in this loop:

sirius-desktop/plugins/org.eclipse.sirius.diagram/src/org/eclipse/sirius/diagram/business/internal/metamodel/helper/LayerHelper.java

Line 373 in 33b42e3

transientLayers.add((AdditionalLayer) layer);

Tested in version 7.1.0