pgsql: Doc: specify aclitem syntax more clearly.

Doc: specify aclitem syntax more clearly.

The previous wording here relied solely on an example to explain
aclitem output format.  Add an actual syntax synopsis and
explanation of the elements to make it clearer.

David Johnston and Tom Lane, per gripe from Eugen Konkov.

Discussion: https://postgr.es/m/170326116972.1876499.18357820037829248593@wrigleys.postgresql.org

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d02cceb85cf1a46a36c36825dd8266a30aed134f

Modified Files
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doc/src/sgml/ddl.sgml | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)