Make CarPrototype implement radar_range

[pastelstoic]

Spider units can optionally have a built-in radar range, but cars and tanks cannot. Please allow non-spider units to have a radar. If possible, allowing this for trains would also be nice.

[Genhis]

This already exists for all vehicles: chunk_exploration_radius

[pastelstoic]

I see. In that case, please add to the documentation that this field and radar_range have the same effect.

[curiosity]

Do note that it's the spider units (e.g. pentapods) that have radar_range. Spider vehicles have one and only chunk_exploration_radius, which is exactly how the vanilla defines it in its prototype code. There is no overlap.

[pastelstoic]

...I may be stupid.

[Bilka]

The descriptions were very lacking anyway, so I've expanded them for 2.0.69.