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

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

wpilibj/src/test/java/edu/wpi/first/wpilibj/SlewRateLimiterTest.java

@@ -1,26 +0,0 @@
-// 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.wpilibj;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertTrue;
-
-import org.junit.jupiter.api.Test;
-
-public class SlewRateLimiterTest {
-  @Test
-  void slewRateLimitTest() {
-    SlewRateLimiter limiter = new SlewRateLimiter(1);
-    Timer.delay(1);
-    assertTrue(limiter.calculate(2) < 2);
-  }
-
-  @Test
-  void slewRateNoLimitTest() {
-    SlewRateLimiter limiter = new SlewRateLimiter(1);
-    Timer.delay(1);
-    assertEquals(limiter.calculate(0.5), 0.5);
-  }
-}