Virtualize applying the attributes in a new OSXApplyAttr() function and simply
store the attribute in its wxDataViewCustomRenderer version so that it could
be reused later in Render().
The attributes now work correctly in wxOSX/Cocoa dataview sample too.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62599 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775