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.cpp

@@ -89,6 +89,10 @@ bool EmuWindow_SDL2::IsOpen() const {
     return is_open;
 }
 
+bool EmuWindow_SDL2::IsShown() const {
+    return is_shown;
+}
+
 void EmuWindow_SDL2::OnResize() {
     int width, height;
     SDL_GetWindowSize(render_window, &width, &height);