When there is a Sort RelNode that references an integer literal, the JDBC adapter converts this to a SQL ORDER BY clause that contains an integer literal as a sort key. Some dialects (most dialects, in fact) wrongly interpret as a reference to a field.
There is ambiguous in the rel-to-sql's converter when meeting `order by constant `.
Here is an example:
But, `ORDER BY 1` may mean 'sort by the first column in the select list' because of SqlConformance#isSortByOrdinal.
I keep this the same semantics, by apply the rule of `CoreRules#SORT_REMOVE_CONSTANT_KEYS`
Should the rel_to_sql's converter support it natively?