Add new C++ Command framework (#1785)

This is the C++ version of #1682.

The old command framework is still available, but will be deprecated.

Due to name conflicts, the new framework is in the frc2 namespace.
Eventually (after the old command framework is removed in a future year)
it will be moved into the main frc namespace.

wpilibc/src/main/native/include/frc2/command/ScheduleCommand.h

@@ -0,0 +1,46 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <wpi/SmallVector.h>
+
+#include "CommandBase.h"
+#include "CommandHelper.h"
+#include "SetUtilities.h"
+
+namespace frc2 {
+/**
+ * Schedules the given commands when this command is initialized.  Useful for
+ * forking off from CommandGroups.  Note that if run from a CommandGroup, the
+ * group will not know about the status of the scheduled commands, and will
+ * treat this command as finishing instantly.
+ */
+class ScheduleCommand : public CommandHelper<CommandBase, ScheduleCommand> {
+ public:
+  /**
+   * Creates a new ScheduleCommand that schedules the given commands when
+   * initialized.
+   *
+   * @param toSchedule the commands to schedule
+   */
+  explicit ScheduleCommand(wpi::ArrayRef<Command*> toSchedule);
+
+  ScheduleCommand(ScheduleCommand&& other) = default;
+
+  ScheduleCommand(const ScheduleCommand& other) = default;
+
+  void Initialize() override;
+
+  bool IsFinished() override;
+
+  bool RunsWhenDisabled() const override;
+
+ private:
+  wpi::SmallVector<Command*, 4> m_toSchedule;
+};
+}  // namespace frc2