pgsql: Fix input of ISO "extended" time format for types time and timet

Fix input of ISO "extended" time format for types time and timetz.

Commit 3e1a373e2 missed teaching DecodeTimeOnly the same "ptype"
manipulations it added to DecodeDateTime.  While likely harmless
at the time, it became a problem after 5b3c59535 added an error check
that ptype must be zero once we exit the parsing loop (that is, there
shouldn't be any unused prefixes).  The consequence was that we'd
reject time or timetz input like T12:34:56 (the "extended" format
per ISO 8601-1:2019), even though that still worked in timestamp
input.

Since this is clearly under-tested code, add test cases covering all
the ISO 8601 time formats.  (Note: although 8601 allows just "Thh",
we have never accepted that, and this patch doesn't change that.
I'm content to leave that as-is because it seems too likely to be
a mistake rather than intended input.  If anyone wants to allow
that, it should be a separate patch anyway, and not back-patched.)

Per bug #18470 from David Perez.  Back-patch to v16 where we
broke it.

Discussion: https://postgr.es/m/18470-34fad4c829106848@postgresql.org

Branch
------
REL_16_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/019ea7675c7722ff7f9016b878feea8e7faac608

Modified Files
--------------
src/backend/utils/adt/datetime.c       |  11 +++
src/test/regress/expected/horology.out | 155 +++++++++++++++++++++++++++++++++
src/test/regress/sql/horology.sql      |  29 ++++++
3 files changed, 195 insertions(+)