[wpilib] Call set(0) rather than disable for stopMotor (#4763)

For PWM motor controllers, this is going to be the fastest way to stop the motor,
as disabling the PWM output will have a small delay due to the motor controller
needing to detect the missing signal.

Note Set(0) is not a safe approach for CAN motor controllers, which may have closed
loop operation, non-% output set() calls, etc.

wpilibj/src/main/java/edu/wpi/first/wpilibj/motorcontrol/PWMMotorController.java

@@ -78,7 +78,7 @@ public abstract class PWMMotorController extends MotorSafety
 
   @Override
   public void stopMotor() {
-    disable();
+    set(0);
   }
 
   @Override