Split the two command implementations into separate libraries (#2012)

This will allow us at the user code side to determine to include old commands, new commands or both.

wpilibNewCommands/src/main/native/cpp/frc2/command/StartEndCommand.cpp

@@ -0,0 +1,27 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2019 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "frc2/command/StartEndCommand.h"
+
+using namespace frc2;
+
+StartEndCommand::StartEndCommand(std::function<void()> onInit,
+                                 std::function<void()> onEnd,
+                                 std::initializer_list<Subsystem*> requirements)
+    : m_onInit{std::move(onInit)}, m_onEnd{std::move(onEnd)} {
+  AddRequirements(requirements);
+}
+
+StartEndCommand::StartEndCommand(const StartEndCommand& other)
+    : CommandHelper(other) {
+  m_onInit = other.m_onInit;
+  m_onEnd = other.m_onEnd;
+}
+
+void StartEndCommand::Initialize() { m_onInit(); }
+
+void StartEndCommand::End(bool interrupted) { m_onEnd(); }