pgsql: Add range_agg with multirange inputs

Add range_agg with multirange inputs

range_agg for normal ranges already existed. A lot of code can be
shared.

Author: Paul Jungwirth <pj(at)illuminatedcomputing(dot)com>
Reviewed-by: Chapman Flack <chap(at)anastigmatix(dot)net>
Discussion: https://www.postgresql.org/message-id/flat/007ef255-35ef-fd26-679c-f97e7a7f30c2(at)illuminatedcomputing(dot)com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7ae1619bc5b1794938c7387a766b8cae34e38d8a

Modified Files
--------------
doc/src/sgml/func.sgml | 5 +++
src/backend/utils/adt/multirangetypes.c | 61 +++++++++++++++++++++++++++
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_aggregate.dat | 3 ++
src/include/catalog/pg_proc.dat | 11 +++++
src/test/regress/expected/multirangetypes.out | 61 +++++++++++++++++++++++++++
src/test/regress/expected/opr_sanity.out | 3 +-
src/test/regress/sql/multirangetypes.sql | 12 ++++++
8 files changed, 156 insertions(+), 2 deletions(-)