pgsql: Fix mishandling of column-level SELECT privileges for join alias

Fix mishandling of column-level SELECT privileges for join aliases. scanNSItemForColumn, expandNSItemAttrs, and ExpandSingleTable would pass the wrong RTE to markVarForSelectPriv when dealing with a join ParseNamespaceItem: they'd pass the join RTE, when what we need to mark is the base table that

pgsql: Fix mishandling of column-level SELECT privileges for join alias

Fix mishandling of column-level SELECT privileges for join aliases. scanNSItemForColumn, expandNSItemAttrs, and ExpandSingleTable would pass the wrong RTE to markVarForSelectPriv when dealing with a join ParseNamespaceItem: they'd pass the join RTE, when what we need to mark is the base table that