pgsql: hstore_plperl: Add CHECK_FOR_INTERRUPTS() in reference-unwinding

hstore_plperl: Add CHECK_FOR_INTERRUPTS() in reference-unwinding loop.

Add CHECK_FOR_INTERRUPTS() to the while loop in plperl_to_hstore()
that dereferences chains of Perl references, so that a circular
reference (e.g. $x = \$x) can be cancelled by the user instead of
spinning indefinitely. (We looked at detecting such circular
references, but it seems more trouble than it's worth.)

This is a follow-up to da82fbb8f, which fixed the same issue in
SV_to_JsonbValue() in jsonb_plperl.

Author: Aleksander Alekseev <aleksander(at)tigerdata(dot)com>
Reviewed-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Discussion: https://postgr.es/m/CAJ7c6TPbjkzUk4qJ5dHvDNEz0hBuFue3A-XWz_=897z+BC+z8A@mail.gmail.com
Backpatch-through: 14

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/4efef9d18e637f5d1e9e09129785d73f5f8619b4

Modified Files
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contrib/hstore_plperl/hstore_plperl.c | 9 +++++++++
1 file changed, 9 insertions(+)