[SPARK-3363][SQL] Type Coercion should support every type to have null value

Type Coercion should support every type to have null value
Yeah, I don't see any reason to over plan for possible extension in the future.  Since this code is the same in both places I think it'd be better to just call findTightestCommonType instead of duplicating it.  If we decide to add more rules in the future we can add a new function that calls this simpler version.