Unify some error messages

We had essentially the same error in several different wordings.
Unify that.

src/backend/utils/adt/json.c

@@ -1186,7 +1186,7 @@ json_object_agg_transfn_worker(FunctionCallInfo fcinfo,
 		if (!json_unique_check_key(&state->unique_check.check, key, 0))
 			ereport(ERROR,
 					errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
-					errmsg("duplicate JSON key %s", key));
+					errmsg("duplicate JSON object key value: %s", key));
 
 		if (skip)
 			PG_RETURN_POINTER(state);
@@ -1349,7 +1349,7 @@ json_build_object_worker(int nargs, Datum *args, bool *nulls, Oid *types,
 			if (!json_unique_check_key(&unique_check.check, key, 0))
 				ereport(ERROR,
 						errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
-						errmsg("duplicate JSON key %s", key));
+						errmsg("duplicate JSON object key value: %s", key));
 
 			if (skip)
 				continue;

src/backend/utils/adt/jsonb_util.c

@@ -1955,7 +1955,7 @@ uniqueifyJsonbObject(JsonbValue *object, bool unique_keys, bool skip_nulls)
 	if (hasNonUniq && unique_keys)
 		ereport(ERROR,
 				errcode(ERRCODE_DUPLICATE_JSON_OBJECT_KEY_VALUE),
-				errmsg("duplicate JSON object key"));
+				errmsg("duplicate JSON object key value"));
 
 	if (hasNonUniq || skip_nulls)
 	{

src/interfaces/ecpg/test/expected/sql-sqljson.stderr

@@ -42,11 +42,11 @@
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_execute on line 33: using PQexec
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: ecpg_check_PQresult on line 33: bad response - ERROR:  duplicate JSON key "1"
+[NO_PID]: ecpg_check_PQresult on line 33: bad response - ERROR:  duplicate JSON object key value: "1"
 [NO_PID]: sqlca: code: 0, state: 00000
-[NO_PID]: raising sqlstate 22030 (sqlcode -400): duplicate JSON key "1" on line 33
+[NO_PID]: raising sqlstate 22030 (sqlcode -400): duplicate JSON object key value: "1" on line 33
 [NO_PID]: sqlca: code: -400, state: 22030
-SQL error: duplicate JSON key "1" on line 33
+SQL error: duplicate JSON object key value: "1" on line 33
 [NO_PID]: ecpg_execute on line 36: query: select json_object ( 1 : 1 , '2' : null , 1 : '2' absent on null without unique keys ); with 0 parameter(s) on connection ecpg1_regression
 [NO_PID]: sqlca: code: 0, state: 00000
 [NO_PID]: ecpg_execute on line 36: using PQexec

src/test/regress/expected/sqljson.out

@@ -254,17 +254,17 @@ SELECT JSON_OBJECT('a': '1', 'b': NULL, 'c': 2 ABSENT ON NULL);
 (1 row)
 
 SELECT JSON_OBJECT(1: 1, '1': NULL WITH UNIQUE);
-ERROR:  duplicate JSON key "1"
+ERROR:  duplicate JSON object key value: "1"
 SELECT JSON_OBJECT(1: 1, '1': NULL ABSENT ON NULL WITH UNIQUE);
-ERROR:  duplicate JSON key "1"
+ERROR:  duplicate JSON object key value: "1"
 SELECT JSON_OBJECT(1: 1, '1': NULL NULL ON NULL WITH UNIQUE RETURNING jsonb);
-ERROR:  duplicate JSON object key
+ERROR:  duplicate JSON object key value
 SELECT JSON_OBJECT(1: 1, '1': NULL ABSENT ON NULL WITH UNIQUE RETURNING jsonb);
-ERROR:  duplicate JSON object key
+ERROR:  duplicate JSON object key value
 SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 NULL ON NULL WITH UNIQUE);
-ERROR:  duplicate JSON key "1"
+ERROR:  duplicate JSON object key value: "1"
 SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 ABSENT ON NULL WITH UNIQUE);
-ERROR:  duplicate JSON key "1"
+ERROR:  duplicate JSON object key value: "1"
 SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 ABSENT ON NULL WITHOUT UNIQUE);
     json_object     
 --------------------
@@ -272,7 +272,7 @@ SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 ABSENT ON NULL WITHOUT UNIQUE);
 (1 row)
 
 SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 ABSENT ON NULL WITH UNIQUE RETURNING jsonb);
-ERROR:  duplicate JSON object key
+ERROR:  duplicate JSON object key value
 SELECT JSON_OBJECT(1: 1, '2': NULL, '1': 1 ABSENT ON NULL WITHOUT UNIQUE RETURNING jsonb);
  json_object 
 -------------
@@ -613,10 +613,10 @@ FROM
 
 SELECT JSON_OBJECTAGG(k: v WITH UNIQUE KEYS)
 FROM (VALUES (1, 1), (1, NULL), (2, 2)) foo(k, v);
-ERROR:  duplicate JSON key "1"
+ERROR:  duplicate JSON object key value: "1"
 SELECT JSON_OBJECTAGG(k: v ABSENT ON NULL WITH UNIQUE KEYS)
 FROM (VALUES (1, 1), (1, NULL), (2, 2)) foo(k, v);
-ERROR:  duplicate JSON key "1"
+ERROR:  duplicate JSON object key value: "1"
 SELECT JSON_OBJECTAGG(k: v ABSENT ON NULL WITH UNIQUE KEYS)
 FROM (VALUES (1, 1), (0, NULL), (3, NULL), (2, 2), (4, NULL)) foo(k, v);
     json_objectagg    
@@ -626,10 +626,10 @@ FROM (VALUES (1, 1), (0, NULL), (3, NULL), (2, 2), (4, NULL)) foo(k, v);
 
 SELECT JSON_OBJECTAGG(k: v WITH UNIQUE KEYS RETURNING jsonb)
 FROM (VALUES (1, 1), (1, NULL), (2, 2)) foo(k, v);
-ERROR:  duplicate JSON object key
+ERROR:  duplicate JSON object key value
 SELECT JSON_OBJECTAGG(k: v ABSENT ON NULL WITH UNIQUE KEYS RETURNING jsonb)
 FROM (VALUES (1, 1), (1, NULL), (2, 2)) foo(k, v);
-ERROR:  duplicate JSON object key
+ERROR:  duplicate JSON object key value
 -- Test JSON_OBJECT deparsing
 EXPLAIN (VERBOSE, COSTS OFF)
 SELECT JSON_OBJECT('foo' : '1' FORMAT JSON, 'bar' : 'baz' RETURNING json);