Fix handling of collations in multi-row VALUES constructs.

Per spec we ought to apply select_common_collation() across the expressions
in each column of the VALUES table.  The original coding was just taking
the first row and assuming it was representative.

This patch adds a field to struct RangeTblEntry to carry the resolved
collations, so initdb is forced for changes in stored rule representation.

src/backend/nodes/readfuncs.c

@@ -1203,6 +1203,7 @@ _readRangeTblEntry(void)
 			break;
 		case RTE_VALUES:
 			READ_NODE_FIELD(values_lists);
+			READ_NODE_FIELD(values_collations);
 			break;
 		case RTE_CTE:
 			READ_STRING_FIELD(ctename);