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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REL9_5_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2af8894c409d0464d4f29449ac39d7d229ccc6ef

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