When a Session is missing a viewpoint, refresh does nothing but no user feedback is provided

[flatombe]

When refreshing a representation through the UI, org.eclipse.sirius.business.api.dialect.command.RefreshRepresentationsCommand is created and executed.

To determine whether the refresh may actually happen, org.eclipse.sirius.business.api.dialect.AbstractRepresentationDialectServices.areRequiredViewpointsSelected(DRepresentation) is called.

When some of the required viewpoints are missing from the session, the refresh does not happen, but there is no feedback to the user that the refresh did not really occur.

Ideally, the refresh action should probably be disabled when it cannot operate, and the UI should explain to the user why that is the case.
At the very least, an error/warning should be logged.