[wpimath] Add SimpleMotorFeedforward::Calculate(velocity, nextVelocity) overload (#3183)

This is often more convenient than using the overload with velocity and
acceleration.

Fixes #3160.

wpimath/src/test/java/edu/wpi/first/math/controller/SimpleMotorFeedforwardTest.java

@@ -0,0 +1,46 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.math.controller;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import edu.wpi.first.math.Matrix;
+import edu.wpi.first.math.Nat;
+import edu.wpi.first.math.VecBuilder;
+import edu.wpi.first.math.numbers.N1;
+import org.junit.jupiter.api.Test;
+
+class SimpleMotorFeedforwardTest {
+  @SuppressWarnings("LocalVariableName")
+  @Test
+  void testCalculate() {
+    double Ks = 0.5;
+    double Kv = 3.0;
+    double Ka = 0.6;
+    double dt = 0.02;
+
+    var A = Matrix.mat(Nat.N1(), Nat.N1()).fill(-Kv / Ka);
+    var B = Matrix.mat(Nat.N1(), Nat.N1()).fill(1.0 / Ka);
+
+    var plantInversion = new LinearPlantInversionFeedforward<N1, N1, N1>(A, B, dt);
+    var simpleMotor = new SimpleMotorFeedforward(Ks, Kv, Ka);
+
+    var r = VecBuilder.fill(2.0);
+    var nextR = VecBuilder.fill(3.0);
+
+    assertEquals(37.524995834325161 + 0.5, simpleMotor.calculate(2.0, 3.0, dt), 0.002);
+    assertEquals(
+        plantInversion.calculate(r, nextR).get(0, 0) + Ks,
+        simpleMotor.calculate(2.0, 3.0, dt),
+        0.002);
+
+    // These won't match exactly. It's just an approximation to make sure they're
+    // in the same ballpark.
+    assertEquals(
+        plantInversion.calculate(r, nextR).get(0, 0) + Ks,
+        simpleMotor.calculate(2.0, 1.0 / dt),
+        2.0);
+  }
+}