tdf#167059 Revert commit f4c2c7c79c

Note: this change will cause tdf#163734 to reoccur on Windows. That
might be fixable by copying the macOS approach and flushing in
"window moved" events. See the following tdf#167059 comment:

https://bugs.documentfoundation.org/show_bug.cgi?id=167059#c27

Change-Id: Id51169dcb9b1ec57a3962f5304fe37e41933cc56
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/187454
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins
Reviewed-by: Patrick Luby <guibomacdev@gmail.com>

vcl/skia/gdiimpl.cxx

@@ -251,7 +251,7 @@ public:
         SetPriority(TaskPriority::SKIA_FLUSH);
 #else
         // We don't want to be swapping before we've painted.
-        SetPriority(TaskPriority::POST_PAINT);
+        SetPriority(TaskPriority::HIGHEST);
 #endif
     }
 #ifndef NDEBUG