pgsql: Document aclitem functions and operators

Document aclitem functions and operators

aclitem functions and operators have been heretofore undocumented.
Fix that. While at it, ensure the non-operator aclitem functions have
pg_description strings.

Does not seem worthwhile to back-patch.

Author: Fabien Coelho, with pg_description from John Naylor, and significant
refactoring and editorialization by me.
Reviewed by: Tom Lane
Discussion: https://postgr.es/m/flat/alpine.DEB.2.21.1808010825490.18204%40lancre

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/c62dd80cdf149e2792b13c13777a539f5abb0370

Modified Files
--------------
doc/src/sgml/func.sgml          | 137 +++++++++++++++++++++++++++++++++++++++-
src/backend/utils/adt/acl.c     |   3 +-
src/include/catalog/pg_proc.dat |   4 +-
3 files changed, 139 insertions(+), 5 deletions(-)