Set focus from LUA code

Like Danoise said I don`t think there is a way to do this directly. The only other thing would be to close the dialog on button press and then have the user re-open after using the pattern editor, but i guess this may defeat the functionality of the GUI anyway.

It may be worth making a request in the API thread here for the future, it sounds like a decent addition:

https://forum.renoise.com/t/the-api-wishlist-thread/29285