public void apply_attrs (AttrIterator iter)
Add attributes to a PangoItem.
The idea is that you have attributes that don't affect itemization, such as font features, so you filter them out using filter, itemize your text, then reapply the attributes to the resulting items using this function.
iter should be positioned before the range of the item, and will be advanced past it. This function is meant to be called in a
loop over the items resulting from itemization, while passing the iter to each call.