[aurorae] Mark the render QQuickWindow as frameless

Summary:
On Wayland aurorae was creating a lot of stress for the system and
basically turning the system unusable in a short time. This was due to
a recursion starting to create OpenGL contexts. The window created a
decoration (aurorae) which created a QQuickWindow. For that KWin creates
an internal window which in turn triggers the creation of a window
decoration and so on and on.

By simply setting the render QQuickWindow as frameless we can prevent
this recursion.

Test Plan: Tested on Wayland and X11. On Wayland the recursion is gone.

Reviewers: KWin, Plasma

Subscribers: plasma-devel, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D6726