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/include/frc2/command/PerpetualCommand.h

@@ -0,0 +1,78 @@
+/*----------------------------------------------------------------------------*/
+/* 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
+
+#ifdef _WIN32
+#pragma warning(push)
+#pragma warning(disable : 4521)
+#endif
+
+#include <memory>
+#include <utility>
+
+#include "CommandBase.h"
+#include "CommandGroupBase.h"
+#include "CommandHelper.h"
+
+namespace frc2 {
+/**
+ * A command that runs another command in perpetuity, ignoring that command's
+ * end conditions.  While this class does not extend {@link CommandGroupBase},
+ * it is still considered a CommandGroup, as it allows one to compose another
+ * command within it; the command instances that are passed to it cannot be
+ * added to any other groups, or scheduled individually.
+ *
+ * <p>As a rule, CommandGroups require the union of the requirements of their
+ * component commands.
+ */
+class PerpetualCommand : public CommandHelper<CommandBase, PerpetualCommand> {
+ public:
+  /**
+   * Creates a new PerpetualCommand.  Will run another command in perpetuity,
+   * ignoring that command's end conditions, unless this command itself is
+   * interrupted.
+   *
+   * @param command the command to run perpetually
+   */
+  explicit PerpetualCommand(std::unique_ptr<Command>&& command);
+
+  /**
+   * Creates a new PerpetualCommand.  Will run another command in perpetuity,
+   * ignoring that command's end conditions, unless this command itself is
+   * interrupted.
+   *
+   * @param command the command to run perpetually
+   */
+  template <class T, typename = std::enable_if_t<std::is_base_of_v<
+                         Command, std::remove_reference_t<T>>>>
+  explicit PerpetualCommand(T&& command)
+      : PerpetualCommand(std::make_unique<std::remove_reference_t<T>>(
+            std::forward<T>(command))) {}
+
+  PerpetualCommand(PerpetualCommand&& other) = default;
+
+  // No copy constructors for command groups
+  PerpetualCommand(const PerpetualCommand& other) = delete;
+
+  // Prevent template expansion from emulating copy ctor
+  PerpetualCommand(PerpetualCommand&) = delete;
+
+  void Initialize() override;
+
+  void Execute() override;
+
+  void End(bool interrupted) override;
+
+ private:
+  std::unique_ptr<Command> m_command;
+};
+}  // namespace frc2
+
+#ifdef _WIN32
+#pragma warning(pop)
+#endif