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.

wpilibOldCommands/src/main/native/include/frc/commands/Scheduler.h

@@ -0,0 +1,100 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2011-2019 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <memory>
+
+#include "frc/ErrorBase.h"
+#include "frc/smartdashboard/Sendable.h"
+#include "frc/smartdashboard/SendableHelper.h"
+
+namespace frc {
+
+class ButtonScheduler;
+class Command;
+class Subsystem;
+
+class Scheduler : public ErrorBase,
+                  public Sendable,
+                  public SendableHelper<Scheduler> {
+ public:
+  /**
+   * Returns the Scheduler, creating it if one does not exist.
+   *
+   * @return the Scheduler
+   */
+  static Scheduler* GetInstance();
+
+  /**
+   * Add a command to be scheduled later.
+   *
+   * In any pass through the scheduler, all commands are added to the additions
+   * list, then at the end of the pass, they are all scheduled.
+   *
+   * @param command The command to be scheduled
+   */
+  void AddCommand(Command* command);
+
+  void AddButton(ButtonScheduler* button);
+
+  /**
+   * Registers a Subsystem to this Scheduler, so that the Scheduler might know
+   * if a default Command needs to be run.
+   *
+   * All Subsystems should call this.
+   *
+   * @param system the system
+   */
+  void RegisterSubsystem(Subsystem* subsystem);
+
+  /**
+   * Runs a single iteration of the loop.
+   *
+   * This method should be called often in order to have a functioning
+   * Command system. The loop has five stages:
+   *
+   * <ol>
+   *   <li>Poll the Buttons</li>
+   *   <li>Execute/Remove the Commands</li>
+   *   <li>Send values to SmartDashboard</li>
+   *   <li>Add Commands</li>
+   *   <li>Add Defaults</li>
+   * </ol>
+   */
+  void Run();
+
+  /**
+   * Removes the Command from the Scheduler.
+   *
+   * @param command the command to remove
+   */
+  void Remove(Command* command);
+
+  void RemoveAll();
+
+  /**
+   * Completely resets the scheduler. Undefined behavior if running.
+   */
+  void ResetAll();
+
+  void SetEnabled(bool enabled);
+
+  void InitSendable(SendableBuilder& builder) override;
+
+ private:
+  Scheduler();
+  ~Scheduler() override;
+
+  Scheduler(Scheduler&&) = default;
+  Scheduler& operator=(Scheduler&&) = default;
+
+  struct Impl;
+  std::unique_ptr<Impl> m_impl;
+};
+
+}  // namespace frc