SplayTreeMap documentation does not say keys are in order

[whesse]

The documentation of the SplayTreeMap class does not say that keys are iterated in order.

The [page]9https://api.dart.dev/stable/2.18.7/dart-collection/dart-collection-library.html) for the collections library links to SplayTreeMap with a statement that it iterates the keys in order, but this is missing from the documentation for the class itself, and from the pages for the key, entries, and value getters, as well as other iterators.

For SplayTreeMap, these methods are marked as overridden, and have their own documentation pages, but on other Map impementations, they just link to the methods on Map, and so don't specify order.

[Cat-sushi]

I saw several people trying to sort by values.