GetClippingBox() implementation relies on wxDCImpl::m_clip[XY][12] being updated in DoSetClippingRegion() but this wasn't done here. Fix this by adding the code to do this to the base class version of this method and calling it from wxGtkPrinterDCImpl. Also, refactor wxGCDCImpl to reuse the same code instead of duplicating it. Closes #14697. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72674 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775