Implement SuspendScreenSaver for Win32

Creating a full-screen SDL renderer on Windows will keep the screensaver
suspended by DirectX, as is default for full-screen DX applications. However,
for applications that render in windowed-mode, the screensaver will
still kick in, even if SDL_DisableScreenSaver() is called or
SDL_HINT_VIDEO_ALLOW_SCREENSAVER is set to 0 (default). Implementing
a SuspendScreenSaver() function for Win32 fixes this behavior.

src/video/windows/SDL_windowsvideo.c

@@ -63,6 +63,15 @@ UpdateWindowFrameUsableWhileCursorHidden(void *userdata, const char *name, const
     }
 }
 
+static void WIN_SuspendScreenSaver(_THIS)
+{
+    if (_this->suspend_screensaver) {
+        SetThreadExecutionState(ES_CONTINUOUS | ES_DISPLAY_REQUIRED);
+    } else {
+        SetThreadExecutionState(ES_CONTINUOUS);
+    }
+}
+
 
 /* Windows driver bootstrap functions */
 
@@ -136,6 +145,7 @@ WIN_CreateDevice(int devindex)
     device->GetDisplayModes = WIN_GetDisplayModes;
     device->SetDisplayMode = WIN_SetDisplayMode;
     device->PumpEvents = WIN_PumpEvents;
+    device->SuspendScreenSaver = WIN_SuspendScreenSaver;
 
     device->CreateSDLWindow = WIN_CreateWindow;
     device->CreateSDLWindowFrom = WIN_CreateWindowFrom;