[wpimath] Move RobotDriveBase::ApplyDeadband() to MathUtil (#3529)

It's a useful function outside of the drive classes.

For backwards compatibility, deprecate (rather than remove) RobotDriveBase.applyDeadband()

wpilibc/src/main/native/cpp/drive/DifferentialDrive.cpp

@@ -11,6 +11,7 @@
 #include <wpi/sendable/SendableBuilder.h>
 #include <wpi/sendable/SendableRegistry.h>
 
+#include "frc/MathUtil.h"
 #include "frc/SpeedController.h"
 
 using namespace frc;