Qt: Implement GBA host and widget

Source/Core/DolphinQt/GBAHost.h

@@ -0,0 +1,28 @@
+// Copyright 2021 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <vector>
+
+#include "Core/Host.h"
+
+namespace HW::GBA
+{
+class Core;
+}  // namespace HW::GBA
+
+class GBAWidgetController;
+
+class GBAHost : public GBAHostInterface
+{
+public:
+  explicit GBAHost(std::weak_ptr<HW::GBA::Core> core);
+  ~GBAHost();
+  void GameChanged() override;
+  void FrameEnded(const std::vector<u32>& video_buffer) override;
+
+private:
+  GBAWidgetController* m_widget_controller{};
+  std::weak_ptr<HW::GBA::Core> m_core;
+};