VideoBackends: Make it possible for PrepareWindow to change the surface

Again, needed for MoltenVK.

Source/Core/Core/Core.cpp

@@ -233,12 +233,13 @@ bool Init(std::unique_ptr<BootParameters> boot, const WindowSystemInfo& wsi)
   Host_UpdateMainFrame();  // Disable any menus or buttons at boot
 
   // Issue any API calls which must occur on the main thread for the graphics backend.
-  g_video_backend->PrepareWindow(wsi);
+  WindowSystemInfo prepared_wsi(wsi);
+  g_video_backend->PrepareWindow(prepared_wsi);
 
   // Start the emu thread
   s_done_booting.Reset();
   s_is_booting.Set();
-  s_emu_thread = std::thread(EmuThread, std::move(boot), wsi);
+  s_emu_thread = std::thread(EmuThread, std::move(boot), prepared_wsi);
   return true;
 }
 

Source/Core/VideoBackends/Vulkan/VideoBackend.h

@@ -18,6 +18,6 @@ public:
   std::string GetName() const override { return "Vulkan"; }
   std::string GetDisplayName() const override { return _trans("Vulkan"); }
   void InitBackendInfo() override;
-  void PrepareWindow(const WindowSystemInfo& wsi) override;
+  void PrepareWindow(WindowSystemInfo& wsi) override;
 };
 }  // namespace Vulkan

Source/Core/VideoBackends/Vulkan/main.cpp

@@ -304,7 +304,7 @@ static bool IsRunningOnMojaveOrHigher()
 }
 #endif
 
-void VideoBackend::PrepareWindow(const WindowSystemInfo& wsi)
+void VideoBackend::PrepareWindow(WindowSystemInfo& wsi)
 {
 #if defined(VK_USE_PLATFORM_MACOS_MVK)
   // This is kinda messy, but it avoids having to write Objective C++ just to create a metal layer.

Source/Core/VideoCommon/VideoBackendBase.h

@@ -47,7 +47,7 @@ public:
 
   // Prepares a native window for rendering. This is called on the main thread, or the
   // thread which owns the window.
-  virtual void PrepareWindow(const WindowSystemInfo& wsi) {}
+  virtual void PrepareWindow(WindowSystemInfo& wsi) {}
 
   static std::string BadShaderFilename(const char* shader_stage, int counter);