pgsql: Support "of", "tzh", and "tzm" format codes.

Support "of", "tzh", and "tzm" format codes.

The upper case versions "OF", "TZH", and "TZM" are already supported,
and all other format codes that are supported in upper case are also
supported in lower case, so we should support these as well for
consistency.

Nitin Jadhav, with a tiny cosmetic change by me. Reviewed by Suraj
Kharage and David Zhang.

Discussion: http://postgr.es/m/CAMm1aWZ-oZyKd75+8D=VJ0sAoSwtdXWLP-MAWD4D8R1Dgandzw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/9dde82899cdf48bd7b2f3d83e4f724ac9ae02c79

Modified Files
--------------
src/backend/utils/adt/formatting.c | 10 ++++-
src/test/regress/expected/timestamptz.out | 65 +++++++++++++++++++++++++++++++
src/test/regress/sql/timestamptz.sql | 22 +++++++++++
3 files changed, 95 insertions(+), 2 deletions(-)