Add --print-fps to enable FPS counter on start

The FPS counter could be enabled/disabled via MOD+i.

Add a command line option to enable it on start. This is consistent with
other features like --turn-screen-off or --fullscreen.

Fixes #468 <https://github.com/Genymobile/scrcpy/issues/468>
PR #3030 <https://github.com/Genymobile/scrcpy/pull/3030>

app/src/screen.h

@@ -35,6 +35,7 @@ struct sc_screen {
         uint16_t width;
         uint16_t height;
         bool fullscreen;
+        bool start_fps_counter;
     } req;
 
     SDL_Window *window;
@@ -93,6 +94,7 @@ struct sc_screen_params {
     bool mipmaps;
 
     bool fullscreen;
+    bool start_fps_counter;
 
     sc_tick buffering_time;
 };