pgsql: Guard against overly-long numeric formatting symbols from locale

Guard against overly-long numeric formatting symbols from locale.

to_char() allocates its output buffer with 8 bytes per formatting
code in the pattern. If the locale's currency symbol, thousands
separator, or decimal or sign symbol is more than 8 bytes long,
in principle we could overrun the output buffer. No such locales
exist in the real world, so it seems sufficient to truncate the
symbol if we do see it's too long.

Reported-by: Xint Code
Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/638232.1776790821@sss.pgh.pa.us
Backpatch-through: 14

Branch
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REL_14_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/8a6f08c0c7c3769ba32e302c95c7950179e5b87e

Modified Files
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src/backend/utils/adt/formatting.c | 61 +++++++++++++++++++++++++++-----------
1 file changed, 43 insertions(+), 18 deletions(-)