[wpiutil] Rename Java package to edu.wpi.first.util (#3431)

This is more consistent with wpimath being edu.wpi.first.math.

wpiutil/src/dev/java/edu/wpi/first/util/DevMain.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.util;
+
+public final class DevMain {
+  /** Main entry point. */
+  public static void main(String[] args) {
+    System.out.println("Hello World!");
+    System.out.println(RuntimeDetector.getPlatformPath());
+  }
+
+  private DevMain() {}
+}