Allows placementoperation to take null for PlacementAlignment so that all snaplines can be shown at the same time on resize operations
Merge remote-tracking branch 'remotes/origin/WpfDesignerAlignmentAllowNull'

Conflicts:
	src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Extensions/SnaplinePlacementBehavior.cs