yuzu: Implement Vulkan frontend

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

src/yuzu_tester/emu_window/emu_window_sdl2_hide.h

@@ -25,6 +25,13 @@ public:
     /// Releases the GL context from the caller thread
     void DoneCurrent() override;
 
+    /// Whether the screen is being shown or not.
+    bool IsShown() const override;
+
+    /// Retrieves Vulkan specific handlers from the window
+    void RetrieveVulkanHandlers(void* get_instance_proc_addr, void* instance,
+                                void* surface) const override;
+
     /// Whether the window is still open, and a close request hasn't yet been sent
     bool IsOpen() const;