DolphinQt: Move gamecube controller ui logic to its own widget

Source/Core/DolphinQt/Config/GamecubeControllersWidget.h

@@ -0,0 +1,39 @@
+// Copyright 2021 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <QWidget>
+
+#include <array>
+
+class QComboBox;
+class QHBoxLayout;
+class QGridLayout;
+class QGroupBox;
+class QPushButton;
+
+class GamecubeControllersWidget final : public QWidget
+{
+  Q_OBJECT
+public:
+  explicit GamecubeControllersWidget(QWidget* parent);
+
+private:
+  void LoadSettings();
+  void SaveSettings();
+
+  void OnGCTypeChanged(int state);
+  void OnGCPadConfigure();
+
+  void CreateLayout();
+  void ConnectWidgets();
+
+  // Gamecube
+  QGroupBox* m_gc_box;
+  QGridLayout* m_gc_layout;
+  std::array<QComboBox*, 4> m_gc_controller_boxes;
+  std::array<QPushButton*, 4> m_gc_buttons;
+  std::array<QHBoxLayout*, 4> m_gc_groups;
+};