Add generics to _ArrayIterator and _ArrayEnumeration

[hduelme]

I added the missing generics to _ArrayIterator and _ArrayEnumeration and to the places they are used.

[ddekany]

The reason FreeMarker doesn't use generics is that it's not backward compatible to add them to public API-s. So it couldn't adopt them. Even though TemplateElement is in principle internal, it's used by some.

[hduelme]

Good to know, I thought TemplateElement was only an internal API. I removed the change to the API.