pgsql: Add overflow checks to money type.

Add overflow checks to money type.

None of the arithmetic functions for the the money type handle
overflow.  This commit introduces several helper functions with
overflow checking and makes use of them in the money type's
arithmetic functions.

Fixes bug #18240.

Reported-by: Alexander Lakhin
Author: Joseph Koshakow
Discussion: https://postgr.es/m/18240-c5da758d7dc1ecf0%40postgresql.org
Discussion: https://postgr.es/m/CAAvxfHdBPOyEGS7s%2Bxf4iaW0-cgiq25jpYdWBqQqvLtLe_t6tw%40mail.gmail.com
Backpatch-through: 12

Branch
------
REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e8dfe0430fad922948f56889a84af41da532c853

Modified Files
--------------
src/backend/utils/adt/cash.c        | 174 +++++++++++++++++++-----------------
src/test/regress/expected/money.out |  19 ++++
src/test/regress/sql/money.sql      |  11 +++
3 files changed, 124 insertions(+), 80 deletions(-)