pgsql: Modernize to_char's Roman-numeral code, fixing overflow problems

Modernize to_char's Roman-numeral code, fixing overflow problems.

int_to_roman() only accepts plain "int" input, which is fine since
we're going to produce '###############' for any value above 3999
anyway.  However, the numeric and int8 variants of to_char() would
throw an error if the given input exceeded the integer range, while
the float-input variants invoked undefined-per-C-standard behavior.
Fix things so that you uniformly get '###############' for out of
range input.

Also add test cases covering this code, plus the equally-untested
EEEE, V, and PL format codes.

Discussion: https://postgr.es/m/2956175.1725831136@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/147bbc90f75794e5522dcbadaf2bbe1af3ce574a

Modified Files
--------------
doc/src/sgml/func.sgml                |  2 +
src/backend/utils/adt/formatting.c    | 92 ++++++++++++++++++++++++++---------
src/test/regress/expected/int8.out    | 50 +++++++++++++++++++
src/test/regress/expected/numeric.out | 87 +++++++++++++++++++++++++++++++++
src/test/regress/sql/int8.sql         |  8 +++
src/test/regress/sql/numeric.sql      | 15 ++++++
6 files changed, 231 insertions(+), 23 deletions(-)