Add --prefer-text option

Expose an option to configure how key/text events are forwarded to the
Android device.

Enabling the option avoids issues when combining multiple keys to enter
special characters, but breaks the expected behavior of alpha keys in
games (typically WASD).

Fixes <https://github.com/Genymobile/scrcpy/issues/650>

app/src/event_converter.h

@@ -14,7 +14,8 @@ enum android_metastate
 convert_meta_state(SDL_Keymod mod);
 
 bool
-convert_keycode(SDL_Keycode from, enum android_keycode *to, uint16_t mod);
+convert_keycode(SDL_Keycode from, enum android_keycode *to, uint16_t mod,
+                bool prefer_text);
 
 enum android_motionevent_buttons
 convert_mouse_buttons(uint32_t state);