Add OTG mode

Add an option --otg to run scrcpy with only physical keyboard and mouse
simulation (HID over AOA), without mirroring and without requiring adb.

To avoid adding complexity into the scrcpy initialization and screen
implementation, OTG mode is implemented totally separately, with a
separate window.

PR #2974 <https://github.com/Genymobile/scrcpy/pull/2974>

app/src/options.h

@@ -112,6 +112,9 @@ struct scrcpy_options {
     uint32_t display_id;
     sc_tick display_buffer;
     sc_tick v4l2_buffer;
+#ifdef HAVE_USB
+    bool otg;
+#endif
     bool show_touches;
     bool fullscreen;
     bool always_on_top;