pgsql: Doc: explain that LIKE et al can be used in ANY (sub-select) etc

Doc: explain that LIKE et al can be used in ANY (sub-select) etc.

This wasn't stated anywhere, and it's perhaps not that obvious,
since we get questions about it from time to time. Also undocumented
was that the parser actually translates these into operators.

Discussion: /messages/by-id/CAFj8pRBkvZ71BqGKZnBBG4=0cKG+s50Dy+DYmrizUKEpAtdc+w@mail.gmail.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a7500cce1ef27a319b3d88d9466f71539c187966

Modified Files
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doc/src/sgml/func.sgml | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)