[Suggestion] Allow all vehicle control variables to have an `input_` prefix

[DrprofLuigi]

This functionality exists with aircraft control surfaces, but it would be nice to have for all inputs.

For example, input_brake would be the players direct input, however brake would be the actual braking action on the vehicle.

This would allow pedals to be linked to the input value, but the output could be VM'd. One use case would be a cruse control where the throttle is set to a value, but then deactivated when the player steps on the gas. Or the airbrake system I am making where the input purges the air out of the system, but the braking requires a certain amount of pressure to disengage.