DiagramMutationElementService#createAllocateEdge should initialize the created AllocationUsage

[gdaniel]

The part of the method that operates on semantic element only (so all of the method at the moment) should also be moved to MetamodelMutationElementService.

This would look like

// DiagramMutationElementService.java

public Element createAllocateEdge(Element source, Element target, Node sourceNode, IEditingContext editingContext, IDiagramService diagramService) {
    var allocateEdge = this.metamodelMutationElementService.createAllocateEdge(source, target);
    this.metamodelMutationElementService.initialize(allocatedEdge);
}

and

// MetamodelMutationElementService.java
public AllocationUsage createAllocationUsage(Element source, Element target) {
    // Current code in DiagramMutationElementService
}

private void addEndToAllocateEdge(AllocationUsage edge, Element end) {
    // Current code in DiagramMutationElementService
}