Avoid overflow in size calculations in formatting.c.

Avoid overflow in size calculations in formatting.c.

A few functions in this file were incautious about multiplying a
possibly large integer by a factor more than 1 and then using it as
an allocation size.  This is harmless on 64-bit systems where we'd
compute a size exceeding MaxAllocSize and then fail, but on 32-bit
systems we could overflow size_t, leading to an undersized
allocation and buffer overrun.  To fix, use palloc_array() or
mul_size() instead of handwritten multiplication.

Reported-by: Sven Klemm <sven@tigerdata.com>
Reported-by: Xint Code
Author: Nathan Bossart <nathandbossart@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Tatsuo Ishii <ishii@postgresql.org>
Security: CVE-2026-6473
Backpatch-through: 14