Summary:
On wayland blur on secondary monitor would not render correctly.

BUG: 393723
Depends on D12452

Test Plan:
 - use more than one output
 - log in in a wayland session
 - open a transparent window (for example: Konsole with transparent and blur enabled profile)
 - drag the window to another screen
 - blurs the content under the window corretly

Reviewers: #kwin, graesslin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: apol, zzag, davidedmundson, kwin, #kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D12678