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_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/b82791c8fc2c6bc9d69f4362d7b7f46b9876fa46

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(-)