Improve support for the layout of empty nodes for the new algorithm

[sbegaudeau]

Preliminary tasks

• [1830] Contribute a first version of the new layout algorithm #1947

Tasks

• Simplify the lifecycle of the diagram layout engine #1970
• Add integration tests for the new diagram layout engine #1971
• Contribute rich data structure for the layout algorithm #1831
• Make node inside label optional #1982
• Improve the svg export to also support new experimental diagram layout data #1980
• Add some details regarding the various layout strategies
• The layout engine should be aware of the different layout strategies (only support free-form layout for now)
• Cleanup DiagramCreationService, removes the use of IRepresentationDescriptionSearchService and IObjectService.