Qt3D: Support selectively exclude some entities from bounding volume computation

Qt3D provides QPickingProxy to override bounding volume computation but Qt 3D just ignores when QPickingProxy does not have QGeometryView.

I am not sure that this is intended behavior because, it is very common for one to want to ignore bounding volume computation for some meshes.

For instance, No one wants to compute bounding volume of a screen quad mesh and complains with warning "findBoundingVolumeComputeData: Position attribute not suited for bounding volume computation" if the vertexPosition attribute is 2D.
Or, many UI components whose size is determined by pixel in shader not world position should be ignored when determining bounding volume for QCamera::viewAll() otherwise the result will be unexpected scene.

I think Qt3D should drop entities with QPickingProxy with null QGeometryView when computing bounding volume instead of continuing to next QBoundingVolume component.

Or, at least, Qt3D should provide another way to exclude some entities from bounding volume computation.