(MP view distance) Take camera zoom into calculation for object culling

As can be seen during today’s msfsofficial airshow, multiplayer/AI planes are
culled too early at long range if the camera zoom is high. Based on hours of
experimental evidence and assumptions: Objects/nodes are culled based on their
screensize without taking camera zoom into the calculation, as if the camera
is at 1x zoom. When zooming in using the drone/showcase cam this causes planes
to go invisible at quite short range while they still fill a large portion of
the screen. For a jet fighter sized plane this distance is roughly 2km. The
workaround for this currently is to make every object of the plane giant by
joining them with invisible boxes, giving visual range up to the multiplayer
limit. (30km+ for AI). See the Thunderbirds demo in the show for an example of
this workaround working. Please make the screensize for object culling use the
actual screensize and not the 1x zoom screensize.