add an interaction ray and make VRInteractionComponent derive from WidgetInteractionComponent so it can also handle UMG widgets

This adds an Interaction Ray (which is visible in VR as ray an in desktop mode as cross. It can be always shown or not shown or only be displayed when hovering over something interactable.

The WidgetInteractionCOmponent uses the same raytraces as the interaction component did before, so there should not be any drawback on performance.