yuzu: Implement Vulkan frontend

Adds a Qt and SDL2 frontend for Vulkan. It also finishes the missing
bits on Vulkan initialization.

src/yuzu_cmd/emu_window/emu_window_sdl2_gl.h

@@ -22,6 +22,10 @@ public:
     /// Releases the GL context from the caller thread
     void DoneCurrent() override;
 
+    /// Ignored in OpenGL
+    void RetrieveVulkanHandlers(void* get_instance_proc_addr, void* instance,
+                                void* surface) const override;
+
     std::unique_ptr<Core::Frontend::GraphicsContext> CreateSharedContext() const override;
 
 private: