Add Ability to select a spline point under surfaces.

**Issue description:**
Is very hard work with splines on complex scenes because the "select point" works like any other actor. So, if you have an scene with a lot of actors and the spline is under the surface you can't select the point because you will select another actor accidentally.

My suggestion to improve the spline workflow is (like the transform gizmo) allow to select splines points under surface if the spline is selected.

**Flax version:**
Any