Extend agtype containment operators (@>, <@) (#1285) (#1419)

This PR is part of the patch originally authored by Josh Innis
 for issue # 282. The work included in this PR is as follows:

 - Enable the usage of left and right containment operators inside
   the cypher queries
 - Extend this operator to be used with scalars
 - Add relevant regression tests

age--1.4.0.sql

@@ -3142,7 +3142,8 @@ PARALLEL SAFE;
 
 CREATE OPERATOR CLASS ag_catalog.gin_agtype_ops
 DEFAULT FOR TYPE agtype USING gin AS
-  OPERATOR 7 @>,
+  OPERATOR 7 @>(agtype, agtype),
+  OPERATOR 8 <@(agtype, agtype),
   OPERATOR 9 ?(agtype, agtype),
   OPERATOR 10 ?|(agtype, agtype),
   OPERATOR 11 ?&(agtype, agtype),

regress/expected/agtype.out

@@ -3058,30 +3058,6 @@ SELECT age_end_id(agtype_in('null'));
 
 (1 row)
 
-SELECT agtype_contains('{"id": 1}','{"id": 1}');
- agtype_contains 
------------------
- t
-(1 row)
-
-SELECT agtype_contains('{"id": 1}','{"id": 2}');
- agtype_contains 
------------------
- f
-(1 row)
-
-SELECT '{"id": 1}'::agtype @> '{"id": 1}';
- ?column? 
-----------
- t
-(1 row)
-
-SELECT '{"id": 1}'::agtype @> '{"id": 2}';
- ?column? 
-----------
- f
-(1 row)
-
 --
 -- Test STARTS WITH, ENDS WITH, and CONTAINS
 --