There isn't any reason to have numberous anchors in the same place,
since we can't maintain docx's non-nesting overlapping. So we reduce
to a single anchor, and have all links pointing to one of the
overlapping anchors point to that one. This changes the behavior from
commit e90c714c7 slightly (use the first anchor instead of the last)
so we change the expected test result.
Note that because this produces a state that has to be set after every
invocation of `parPartToInlines`, we make the main function into a
primed subfunction `parPartToInlines'`, and make `parPartToInlines` a
wrapper around that.
