enableAltitude and heightFactor support for GL layers

[joric]

Related to #2486. Pulled from this comment #2486 (comment) as a separate issue for tracking.

I need to disable parallax effect for the top view, it was a big part of UX. This worked for VectorLayer but doesn't work for PointLayer:

if (enableAltitude && autoAltitude) {
  markerLayer.setOptions({enableAltitude: map.getPitch()!=0});
}

See https://joric.github.io/maps/fallout-london/ (VectorLayer) vs https://joric.github.io/stalker/ (PointLayer)

Also heightFactor doesn't seem to work AT ALL, even as a static property. It would be great to change heightFactor dynamically too.