fdo#74424 Use Window::GetOutDev() to access ImplGetGraphics()

Part of the decoupling of Window from OutputDevice. We now get
the Window's OutputDevice instance and manipulate this. Do not rely
on the inherited function.

Conflicts:
	vcl/source/window/window2.cxx

Change-Id: I964596bb6457ccb24e69bad15c497dbf97e5880f
Reviewed-on: https://gerrit.libreoffice.org/7789
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>