as part of a longer-term goal of doing our
widget rendering only inside a top-level render-
context.

I moved all of the OutputDevice-related code that existed in vcl::Window
into a new subclass of OutputDevice called WindowOutputDevice.

Notes for further work

(*) not sure why we are getting an 1x1 surface in
    SvpSalGraphics::releaseCairoContext, but to fix it I clamp
    the size there

(*) might have to dump VCLXDevice, and move it's code down into VCLXWindow and VCLXVirtualDevice

(*) can we remove use of VCLXDevice in other places, in favour of just talking to the VCL code?

Change-Id: I105946377f5322677d6f7d0c1c23847178a720b6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/113204
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>