lcl: TUpDown: implemented preferred size

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@46774 4005530d-fff6-0310-9dd1-cebe43e6787f
lcl: TUpDown: comments

git-svn-id: http://svn.freepascal.org/svn/lazarus/trunk@46775 4005530d-fff6-0310-9dd1-cebe43e6787f