[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.

[DonBruce64]

I can do this, but it'll have to wait for the VM back-end overhaul, since those cause significant lag right now on servers, and me adding these changes will add a bunch of "default" VMs for converting inputs to actuals, which will just make the lag worse.

[DonBruce64]

Yet another variable request that needs CVs to work properly.