[wpimath] Move SlewRateLimiter from wpilib to wpimath (#3399)

Timer was replaced with wpi::Now() to avoid a dependency on other wpilib
classes.

wpimath/src/test/java/edu/wpi/first/math/filter/SlewRateLimiterTest.java

@@ -0,0 +1,35 @@
+// 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.filter;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import edu.wpi.first.wpiutil.WPIUtilJNI;
+import org.junit.jupiter.api.Test;
+
+public class SlewRateLimiterTest {
+  @Test
+  void slewRateLimitTest() {
+    WPIUtilJNI.enableMockTime();
+
+    var limiter = new SlewRateLimiter(1);
+    WPIUtilJNI.setMockTime(1000000L);
+    assertTrue(limiter.calculate(2) < 2);
+
+    WPIUtilJNI.setMockTime(0L);
+  }
+
+  @Test
+  void slewRateNoLimitTest() {
+    WPIUtilJNI.enableMockTime();
+
+    var limiter = new SlewRateLimiter(1);
+    WPIUtilJNI.setMockTime(1000000L);
+    assertEquals(limiter.calculate(0.5), 0.5);
+
+    WPIUtilJNI.setMockTime(0L);
+  }
+}