pgsql: Back-patch addition of stack overflow and interrupt checks for l

Back-patch addition of stack overflow and interrupt checks for lquery.

Experimentation shows that it's not hard at all to drive the
old implementation of "ltree ~ lquery" match to stack overflow,
so throw in a check_stack_depth() call, as I just did in HEAD.

I wasn't able to make it take a long time, because all the
pathological cases I tried hit stack overflow first; but
I bet there are some others that do take a long time, so add
CHECK_FOR_INTERRUPTS() too.

Discussion: https://postgr.es/m/CAP_rww=waX2Oo6q+MbMSiZ9ktdj6eaJj0cQzNu=Ry2cCDij5fw@mail.gmail.com

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/94c9152dc880a8b1d1223c885d6d56d33e417b57

Modified Files
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contrib/ltree/lquery_op.c | 7 +++++++
1 file changed, 7 insertions(+)