Fix IME popups

[chrisduerr]

Currently IME popups are not rendered at all, since neither InputMethodHandler::new_popup nor InputMethodHandler::dismiss_popup are properly implemented. The only function which is properly implemented is InputMethodHandler::parent_geometry, which is not actually needed at all.

This trait implementation should be fixed to be sure IME works properly, though currently there's not a lot of IMEs that would be particularly useful to have on a phone anyway.