I have a patch that adds another group of candidate types to
BuiltinCandidateTypeSet. Currently two styles are in use: the older
begin/end pairs and the newer iterator_range approach. I think the
group of candidates that I want to add should use iterator ranges,
but I'd also like to consolidate the handling of the new candidates
with some existing code that uses begin/end pairs. This patch therefore
converts the begin/end pairs to iterator ranges as a first step.
No functional change intended.