yuzu_cmd: Split emu_window OpenGL implementation into its own file

src/yuzu_cmd/emu_window/emu_window_sdl2_gl.h

@@ -0,0 +1,34 @@
+// Copyright 2019 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include "core/frontend/emu_window.h"
+#include "yuzu_cmd/emu_window/emu_window_sdl2.h"
+
+class EmuWindow_SDL2_GL final : public EmuWindow_SDL2 {
+public:
+    explicit EmuWindow_SDL2_GL(bool fullscreen);
+    ~EmuWindow_SDL2_GL();
+
+    /// Swap buffers to display the next frame
+    void SwapBuffers() override;
+
+    /// Makes the graphics context current for the caller thread
+    void MakeCurrent() override;
+
+    /// Releases the GL context from the caller thread
+    void DoneCurrent() override;
+
+    std::unique_ptr<Core::Frontend::GraphicsContext> CreateSharedContext() const override;
+
+private:
+    /// Whether the GPU and driver supports the OpenGL extension required
+    bool SupportsRequiredGLExtensions();
+
+    using SDL_GLContext = void*;
+    /// The OpenGL context associated with the window
+    SDL_GLContext gl_context;
+};