TAChart: Allow assignment of TFPCustomFont to Font property of canvas drawer

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41892 4005530d-fff6-0310-9dd1-cebe43e6787f
TAChart: Add TDiaFontDecorator

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41893 4005530d-fff6-0310-9dd1-cebe43e6787f
TAChart: Minor refactoring of drawer canvas setters

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@41894 4005530d-fff6-0310-9dd1-cebe43e6787f