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/scrcpy.c

@@ -42,6 +42,7 @@ static struct input_manager input_manager = {
     .controller = &controller,
     .video_buffer = &video_buffer,
     .screen = &screen,
+    .prefer_text = false, // initialized later
 };
 
 // init SDL and set appropriate hints
@@ -414,6 +415,8 @@ scrcpy(const struct scrcpy_options *options) {
         show_touches_waited = true;
     }
 
+    input_manager.prefer_text = options->prefer_text;
+
     ret = event_loop(options->display, options->control);
     LOGD("quit...");