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
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/34e9dce69c4687f8c22831d6b0a1f65fa40c83b1

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(-)