[wpimath] Move Java classes to edu.wpi.first.math (#3316)

wpimath/src/main/java/edu/wpi/first/math/Num.java

@@ -0,0 +1,15 @@
+// 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;
+
+/** A number expressed as a java class. */
+public abstract class Num {
+  /**
+   * The number this is backing.
+   *
+   * @return The number represented by this class.
+   */
+  public abstract int getNum();
+}