pgsql: Add trim_array() function.

Add trim_array() function.

This has been in the SQL spec since 2008. It's a pretty thin
wrapper around the array slice functionality, but the spec
says we should have it, so here it is.

Vik Fearing, reviewed by Dian Fay

Discussion: https://postgr.es/m/fc92ce17-9655-8ff1-c62a-4dc4c8ccd815@postgresfriends.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0a687c8f103d217ff1ca8c34a644b380d89bb0ad

Modified Files
--------------
doc/src/sgml/func.sgml | 18 +++++++++++++++
src/backend/catalog/sql_features.txt | 2 +-
src/backend/utils/adt/arrayfuncs.c | 43 ++++++++++++++++++++++++++++++++++++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 3 +++
src/test/regress/expected/arrays.out | 21 ++++++++++++++++++
src/test/regress/sql/arrays.sql | 13 +++++++++++
7 files changed, 100 insertions(+), 2 deletions(-)