Position and size the window on first frame

The optimal initial size was computed from the expected dimensions, sent
immediately by the server before encoding any video frame.

However, the actual frame size may be different, for example when the
device encoder does not support the requested size.

To always handle this case properly, position and size the window only
once the first frame size is known.

PR #2947 <https://github.com/Genymobile/scrcpy/pull/2947>

app/src/screen.h

@@ -28,6 +28,15 @@ struct sc_screen {
     struct sc_video_buffer vb;
     struct fps_counter fps_counter;
 
+    // The initial requested window properties
+    struct {
+        int16_t x;
+        int16_t y;
+        uint16_t width;
+        uint16_t height;
+        bool fullscreen;
+    } req;
+
     SDL_Window *window;
     SDL_Renderer *renderer;
     SDL_Texture *texture;