VideoBackends: Pass window system info from host on creation

Source/Core/Common/WindowSystemInfo.h

@@ -0,0 +1,35 @@
+// Copyright 2018 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#pragma once
+
+enum class WindowSystemType
+{
+  Headless,
+  Windows,
+  MacOS,
+  Android,
+  X11,
+  Wayland
+};
+
+struct WindowSystemInfo
+{
+  WindowSystemInfo() = default;
+  WindowSystemInfo(WindowSystemType type_, void* display_connection_, void* render_surface_)
+      : type(type_), display_connection(display_connection_), render_surface(render_surface_)
+  {
+  }
+
+  // Window system type. Determines which GL context or Vulkan WSI is used.
+  WindowSystemType type = WindowSystemType::Headless;
+
+  // Connection to a display server. This is used on X11 and Wayland platforms.
+  void* display_connection = nullptr;
+
+  // Render surface. This is a pointer to the native window handle, which depends
+  // on the platform. e.g. HWND for Windows, Window for X11. If the surface is
+  // set to nullptr, the video backend will run in headless mode.
+  void* render_surface = nullptr;
+};