[wpimath] Replace Speeds with Velocities (#8479)

I left "free speed" alone since that's the technical term for it. In
general, velocity is a vector quantity, and speed is a magnitude (i.e.,
a strictly positive value).

This PR also replaces the speed verbiage in MotorController with duty
cycle.

Fixes #8423.

robotpyExamples/SwerveBot/robot.py

@@ -18,8 +18,8 @@ class MyRobot(wpilib.TimedRobot):
         self.swerve = drivetrain.Drivetrain()
 
         # Slew rate limiters to make joystick inputs more gentle; 1/3 sec from 0 to 1.
-        self.xspeedLimiter = wpimath.SlewRateLimiter(3)
-        self.yspeedLimiter = wpimath.SlewRateLimiter(3)
+        self.xvelocityLimiter = wpimath.SlewRateLimiter(3)
+        self.yvelocityLimiter = wpimath.SlewRateLimiter(3)
         self.rotLimiter = wpimath.SlewRateLimiter(3)
 
     def autonomousPeriodic(self) -> None:
@@ -30,23 +30,23 @@ class MyRobot(wpilib.TimedRobot):
         self.driveWithJoystick(True)
 
     def driveWithJoystick(self, fieldRelative: bool) -> None:
-        # Get the x speed. We are inverting this because Xbox controllers return
+        # Get the x velocity. We are inverting this because Xbox controllers return
         # negative values when we push forward.
-        xSpeed = (
-            -self.xspeedLimiter.calculate(
+        xVelocity = (
+            -self.xvelocityLimiter.calculate(
                 wpimath.applyDeadband(self.controller.getLeftY(), 0.02)
             )
-            * drivetrain.kMaxSpeed
+            * drivetrain.kMaxVelocity
         )
 
-        # Get the y speed or sideways/strafe speed. We are inverting this because
+        # Get the y velocity or sideways/strafe velocity. We are inverting this because
         # we want a positive value when we pull to the left. Xbox controllers
         # return positive values when you pull to the right by default.
-        ySpeed = (
-            -self.yspeedLimiter.calculate(
+        yVelocity = (
+            -self.yvelocityLimiter.calculate(
                 wpimath.applyDeadband(self.controller.getLeftX(), 0.02)
             )
-            * drivetrain.kMaxSpeed
+            * drivetrain.kMaxVelocity
         )
 
         # Get the rate of angular rotation. We are inverting this because we want a
@@ -57,7 +57,7 @@ class MyRobot(wpilib.TimedRobot):
             -self.rotLimiter.calculate(
                 wpimath.applyDeadband(self.controller.getRightX(), 0.02)
             )
-            * drivetrain.kMaxAngularSpeed
+            * drivetrain.kMaxAngularVelocity
         )
 
-        self.swerve.drive(xSpeed, ySpeed, rot, fieldRelative, self.getPeriod())
+        self.swerve.drive(xVelocity, yVelocity, rot, fieldRelative, self.getPeriod())