Currently, internal on screen display windows have the bypass window
manager hint set. If that hint is set, the osds must place themselves,
but they don't do it.

As far as I know, there is no any reason why internal OSDs have that
flag set.

By removing the Qt::BypassWindowManagerHint flag, we let kwin core
know that it's okay to place internal OSD windows.

BUG: 400675


(cherry picked from commit 4559d303)