Return position when poco invoke input function of airtest

[stcnchenxin]

Sometimes i want to use the position when use poco.click() for some reason (like calculate, or record), i must use poco.get_position() to get position (and it can be more trouble when use poco.use_render_resolution()).

And in the statement of pocofw.py and airtest, the click/touch function always return the position, it seems confuse that remove that return statement when implement AirtestInput interface.