Problem related to the feature
A cast operation from a character type to another character type that has a different collator must be evaluated as not monotonic. Currently this is not the case.
This has an impact e.g. in SortProjectTransposeRule, since we can incorrectly transpose a sort after a projection than contains such a cast, and we end up with a plan that will return a different result than the original one (it is not the same casting and then sorting; than sorting and then casting).