Fix drawing of items with custom background in wxGenericListCtrl.

Fix drawing of items with custom background in wxGenericListCtrl.

This was broken by the changes of r64879 which erroneously used
wxRendererNative::DrawItemSelectionRect() even for the non-selected items.

Now only use DrawItemSelectionRect() for the selected items to make them
appear natively while drawing the non-selected items with custom background
colour ourselves.

Also refactor the code to avoid (the not quite and hence especially
pernicious) duplication between wxListLineData::Draw() and DrawInReportMode():
rename SetAttributes() to ApplyAttributes() and draw the item background in
this function now instead of doing it in both Draw() and DrawInReportMode().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65541 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775