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/InstantCommand.cpp

@@ -0,0 +1,22 @@
+/*----------------------------------------------------------------------------*/
+/* 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/InstantCommand.h"
+
+using namespace frc2;
+
+InstantCommand::InstantCommand(std::function<void()> toRun,
+                               std::initializer_list<Subsystem*> requirements)
+    : m_toRun{std::move(toRun)} {
+  AddRequirements(requirements);
+}
+
+InstantCommand::InstantCommand() : m_toRun{[] {}} {}
+
+void InstantCommand::Initialize() { m_toRun(); }
+
+bool InstantCommand::IsFinished() { return true; }