[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()

wpimath/src/main/native/include/frc/MathUtil.h

@@ -10,6 +10,15 @@
 
 namespace frc {
 
+/**
+ * Returns 0.0 if the given value is within the specified range around zero.
+ * The remaining range between the deadband and 1.0 is scaled from 0.0 to 1.0.
+ *
+ * @param value    Value to clip.
+ * @param deadband Range around zero.
+ */
+double ApplyDeadband(double value, double deadband);
+
 /**
  * Returns modulus of input.
  *