typedefs.list glitches

I just completed the v15 pre-beta pgindent run. It went reasonably
smoothly, but I had to hack up typedefs.list a little bit compared
to the version downloaded from the buildfarm.

* The buildfarm's list is missing
pg_md5_ctx
pg_sha1_ctx
pg_sha224_ctx
pg_sha256_ctx
pg_sha384_ctx
pg_sha512_ctx
which are certainly used, but only in some src/common files
that are built only in non-OpenSSL builds. So evidently,
every buildfarm member that's contributing to the typedefs list
builds with OpenSSL. That wouldn't surprise me, except that
my own animal sifaka should be filling that gap. Looking at
its latest attempt[1], it seems to be generating an empty list,
which I guess means that our recipe for extracting typedefs
doesn't work on macOS/arm64. I shall investigate.

* The buildfarm's list includes "value_type", which is surely
not typedef'd anywhere in our code, and that is messing up
some formatting involving JsonIsPredicate.value_type.
I suppose that is coming from some system header where it is
a typedef on some machines (komodoensis and lorikeet report it,
which seems like an odd pairing). I think the best thing to
do here is rename that field while we still can, perhaps to
item_type. Thoughts?

regards, tom lane

[1] https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=sifaka&dt=2022-05-11%2020%3A21%3A15