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.h

@@ -21,6 +21,9 @@ public:
     /// Whether the window is still open, and a close request hasn't yet been sent
     bool IsOpen() const;
 
+    /// Returns if window is shown (not minimized)
+    bool IsShown() const override;
+
 protected:
     /// Called by PollEvents when a key is pressed or released.
     void OnKeyEvent(int key, u8 state);