Account for text attrs in generic wxDataViewCtrl's renderers.

Account for text attrs in generic wxDataViewCtrl's renderers.

When determining cell content's size, GetSize() measured the text using
wxDataViewCtrl's font, even though it could be renderer in bold or
italics.

Corrected by setting the attributes - and not only the value - prior to
GetSize() calls, and by using the right font in GetTextExtent() calls.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65949 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775