Summary:
as showEvent is too soon, create the plasma surface on
:Expose event, and reposition the surface

Test Plan: krunner is correctly positioned with correct blur and shadows

Reviewers: #plasma, #plasma_on_wayland, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: hein, davidedmundson, graesslin, plasma-devel

Tags: #plasma_on_wayland

Differential Revision: https://phabricator.kde.org/D5748