Implement hatched/stippled pens/brushes in wxGraphicsContext for Cairo.

Refactor the pen/brushes classes to introduce a common base class for them
containing their colour and hatch pattern and stipple bitmap, if any.

And actually create the hatched pattern and use it.

Closes #11981.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71906 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775