Add support_range to LuaEntityPrototype

[thebrick448]

Currently, support_range is missing from LuaEntityPrototype. The only way to get support_range is to capture it from rail-ramps and rail-supports during the data phase, and cache it for runtime.

Adding this property to LuaEntityPrototype will allow me to more easily access it when programmatically building properly supported elevated railways.

[boskid]

Ok. For 2.0.67 added LuaEntityPrototype::support_range read for RailSupport and RailRamp. Also added LuaEntity::rail_length that may be useful.