tdf#92982 vcl rendercontext: set buffer size in ImplHandleResize()

Instead of in PaintHelper::StartBufferedPaint(). If the buffer size is
set to match the size of a sub-widget (for which the paint was
triggered), then client using the buffer as a persistent vdev are unable
to paint at arbitrary locations.

For example, if we painted the ruler, then the blinking cursor won't be
able to paint to the SwEditWin area.

Change-Id: Iba07070baafb5b802fc6da200696611afd2010d7

vcl/source/window/paint.cxx

@@ -125,9 +125,6 @@ void PaintHelper::StartBufferedPaint()
     // Remember what was the map mode of m_aPaintRect.
     m_aPaintRectMapMode = m_pWindow->GetMapMode();
 
-    // update the output size now, after all the settings were copied
-    pFrameData->mpBuffer->SetOutputSize(m_pWindow->GetOutputSize());
-
     // we need to remember the mnOutOffX / mnOutOffY, but actually really
     // set it just temporarily for the subwidgets - so we are setting it here
     // only to remember the value & to be able to pass it to the descendants

vcl/source/window/winproc.cxx

@@ -35,6 +35,7 @@
 #include <vcl/help.hxx>
 #include <vcl/dockwin.hxx>
 #include <vcl/menu.hxx>
+#include <vcl/virdev.hxx>
 #include <touch/touch.h>
 
 #include <svdata.hxx>
@@ -1714,6 +1715,12 @@ void ImplHandleResize( vcl::Window* pWindow, long nNewWidth, long nNewHeight )
             }
             else
                 pWindow->ImplGetWindowImpl()->mbCallResize = true;
+
+            if (pWindow->SupportsDoubleBuffering() && pWindow->ImplGetWindowImpl()->mbFrame)
+            {
+                // Propagate resize for the frame's buffer.
+                pWindow->ImplGetWindowImpl()->mpFrameData->mpBuffer->SetOutputSizePixel(pWindow->GetOutputSizePixel());
+            }
         }
     }