Primary motivation for this change is the `VERIFY(icu_success(status))`
line in `Segmenter::create()` that was failing on multiple systems and
where we had to ask people to apply a patch to even know what the error
was.
Since this seems to be a recurring problem, let's just add a little
helper function and print the error codes returned by library calls.
Some callers need the raw nul-terminated c-string in this callback, to
pass to some other ICU method. But other callers will want a StringView.
We know the length already in `icu_string_enumeration_to_list`, so let's
just pass it along to avoid `strlen`.
We were manually doing this for the calendar keyword, and would need to
do so for the collation keyword as well. I wasn't aware of this API
originally, so let's start using it.
