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/button/Button.cpp

@@ -0,0 +1,57 @@
+/*----------------------------------------------------------------------------*/
+/* 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/button/Button.h"
+
+using namespace frc2;
+
+Button::Button(std::function<bool()> isPressed) : Trigger(isPressed) {}
+
+Button Button::WhenPressed(Command* command, bool interruptible) {
+  WhenActive(command, interruptible);
+  return *this;
+}
+
+Button Button::WhenPressed(std::function<void()> toRun) {
+  WhenActive(std::move(toRun));
+  return *this;
+}
+
+Button Button::WhileHeld(Command* command, bool interruptible) {
+  WhileActiveContinous(command, interruptible);
+  return *this;
+}
+
+Button Button::WhileHeld(std::function<void()> toRun) {
+  WhileActiveContinous(std::move(toRun));
+  return *this;
+}
+
+Button Button::WhenHeld(Command* command, bool interruptible) {
+  WhileActiveOnce(command, interruptible);
+  return *this;
+}
+
+Button Button::WhenReleased(Command* command, bool interruptible) {
+  WhenInactive(command, interruptible);
+  return *this;
+}
+
+Button Button::WhenReleased(std::function<void()> toRun) {
+  WhenInactive(std::move(toRun));
+  return *this;
+}
+
+Button Button::ToggleWhenPressed(Command* command, bool interruptible) {
+  ToggleWhenActive(command, interruptible);
+  return *this;
+}
+
+Button Button::CancelWhenPressed(Command* command) {
+  CancelWhenActive(command);
+  return *this;
+}