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
------
master

Details
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https://git.postgresql.org/pg/commitdiff/22b0ccd65d275d227a7d911aede12d34e1b5dfc9

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(-)