TAChart: Allow assignment of TFPCustomBrush to Brush property of canvas drawer

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41890 4005530d-fff6-0310-9dd1-cebe43e6787f
TAChart: Add TDiaBrushDecorator class

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41891 4005530d-fff6-0310-9dd1-cebe43e6787f