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

include/wx/dataview.h

@@ -172,6 +172,9 @@ public:
 
     bool IsDefault() const { return !(HasColour() || HasFont()); }
 
+    // Return the font based on the given one with this attribute applied to it.
+    wxFont GetEffectiveFont(const wxFont& font) const;
+
 private:
     wxColour m_colour;
     bool     m_bold;