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.

wpilibOldCommands/src/main/native/cpp/buttons/Trigger.cpp

@@ -0,0 +1,71 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2011-2019 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 "frc/buttons/Button.h"
+#include "frc/buttons/CancelButtonScheduler.h"
+#include "frc/buttons/HeldButtonScheduler.h"
+#include "frc/buttons/PressedButtonScheduler.h"
+#include "frc/buttons/ReleasedButtonScheduler.h"
+#include "frc/buttons/ToggleButtonScheduler.h"
+#include "frc/smartdashboard/SendableBuilder.h"
+
+using namespace frc;
+
+Trigger::Trigger(const Trigger& rhs) : SendableHelper(rhs) {}
+
+Trigger& Trigger::operator=(const Trigger& rhs) {
+  SendableHelper::operator=(rhs);
+  m_sendablePressed = false;
+  return *this;
+}
+
+Trigger::Trigger(Trigger&& rhs)
+    : SendableHelper(std::move(rhs)),
+      m_sendablePressed(rhs.m_sendablePressed.load()) {
+  rhs.m_sendablePressed = false;
+}
+
+Trigger& Trigger::operator=(Trigger&& rhs) {
+  SendableHelper::operator=(std::move(rhs));
+  m_sendablePressed = rhs.m_sendablePressed.load();
+  rhs.m_sendablePressed = false;
+  return *this;
+}
+
+bool Trigger::Grab() { return Get() || m_sendablePressed; }
+
+void Trigger::WhenActive(Command* command) {
+  auto pbs = new PressedButtonScheduler(Grab(), this, command);
+  pbs->Start();
+}
+
+void Trigger::WhileActive(Command* command) {
+  auto hbs = new HeldButtonScheduler(Grab(), this, command);
+  hbs->Start();
+}
+
+void Trigger::WhenInactive(Command* command) {
+  auto rbs = new ReleasedButtonScheduler(Grab(), this, command);
+  rbs->Start();
+}
+
+void Trigger::CancelWhenActive(Command* command) {
+  auto cbs = new CancelButtonScheduler(Grab(), this, command);
+  cbs->Start();
+}
+
+void Trigger::ToggleWhenActive(Command* command) {
+  auto tbs = new ToggleButtonScheduler(Grab(), this, command);
+  tbs->Start();
+}
+
+void Trigger::InitSendable(SendableBuilder& builder) {
+  builder.SetSmartDashboardType("Button");
+  builder.SetSafeState([=]() { m_sendablePressed = false; });
+  builder.AddBooleanProperty("pressed", [=]() { return Grab(); },
+                             [=](bool value) { m_sendablePressed = value; });
+}