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/NotifierCommand.h

@@ -0,0 +1,53 @@
+/*----------------------------------------------------------------------------*/
+/* 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 <frc/Notifier.h>
+
+#include <units/units.h>
+
+#include "CommandBase.h"
+#include "CommandHelper.h"
+
+namespace frc2 {
+/**
+ * A command that starts a notifier to run the given runnable periodically in a
+ * separate thread. Has no end condition as-is; either subclass it or use {@link
+ * Command#withTimeout(double)} or
+ * {@link Command#withInterrupt(BooleanSupplier)} to give it one.
+ *
+ * <p>WARNING: Do not use this class unless you are confident in your ability to
+ * make the executed code thread-safe.  If you do not know what "thread-safe"
+ * means, that is a good sign that you should not use this class.
+ */
+class NotifierCommand : public CommandHelper<CommandBase, NotifierCommand> {
+ public:
+  /**
+   * Creates a new NotifierCommand.
+   *
+   * @param toRun        the runnable for the notifier to run
+   * @param period       the period at which the notifier should run
+   * @param requirements the subsystems required by this command
+   */
+  NotifierCommand(std::function<void()> toRun, units::second_t period,
+                  std::initializer_list<Subsystem*> requirements);
+
+  NotifierCommand(NotifierCommand&& other);
+
+  NotifierCommand(const NotifierCommand& other);
+
+  void Initialize() override;
+
+  void End(bool interrupted) override;
+
+ private:
+  std::function<void()> m_toRun;
+  frc::Notifier m_notifier;
+  units::second_t m_period;
+};
+}  // namespace frc2