Place arbitrary UE Actors sensibly on the globe

[kring]

We need a way to place non-Cesium Actors on a globe, which is weird because it has huge coordinate values and no consistent "up" direction.

Hopefully this can be done via an ActorComponent. The component would:

• Allow the Actor's position to be specified using longitude/latitude/height, double-precision Cartesian coordinates, or just using normal UE world coordinates if desired.
• Orient the Actor so that its local up is aligned with the WGS84 ellipsoid's local up at that position. And then the normal UE orientation would apply from there.
• Optionally adjust the object's height relative to the terrain at that location (see Clamp points to terrain cesium-native#72).