[build] Add package declaration check to checkstyle (#2446)

Co-authored-by: Austin Shalit <austinshalit@gmail.com>

myRobot/src/main/java/frc/robot/Main.java

@@ -0,0 +1,24 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018-2020 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+package frc.robot;
+
+import edu.wpi.first.wpilibj.RobotBase;
+
+public final class Main {
+  private Main() {
+  }
+
+  /**
+   * Main initialization function. Do not perform any initialization here.
+   *
+   * <p>If you change your main robot class, change the parameter type.
+   */
+  public static void main(String... args) {
+    RobotBase.startRobot(MyRobot::new);
+  }
+}