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/options.c

@@ -63,4 +63,5 @@ const struct scrcpy_options scrcpy_options_default = {
     .select_tcpip = false,
     .select_usb = false,
     .cleanup = true,
+    .start_fps_counter = false,
 };