[cmd2] Move .cpp files to subproject source root (#8967)

This matches all of the other subprojects.

Signed-off-by: Zach Harel <zach@zharel.me>

commandsv2/src/main/native/cpp/FunctionalCommand.cpp

@@ -0,0 +1,37 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#include "wpi/commands2/FunctionalCommand.hpp"
+
+#include <utility>
+
+using namespace wpi::cmd;
+
+FunctionalCommand::FunctionalCommand(std::function<void()> onInit,
+                                     std::function<void()> onExecute,
+                                     std::function<void(bool)> onEnd,
+                                     std::function<bool()> isFinished,
+                                     Requirements requirements)
+    : m_onInit{std::move(onInit)},
+      m_onExecute{std::move(onExecute)},
+      m_onEnd{std::move(onEnd)},
+      m_isFinished{std::move(isFinished)} {
+  AddRequirements(requirements);
+}
+
+void FunctionalCommand::Initialize() {
+  m_onInit();
+}
+
+void FunctionalCommand::Execute() {
+  m_onExecute();
+}
+
+void FunctionalCommand::End(bool interrupted) {
+  m_onEnd(interrupted);
+}
+
+bool FunctionalCommand::IsFinished() {
+  return m_isFinished();
+}