camel-case iteratorsize and iteratoreltype

[JeffBezanson]

This matches other traits better.

[ararslan]

Will there be any possibility of a performance regression since the functions are no longer precompiled?

[JeffBezanson]

We need to update the precompile files anyway (#24666).

[nalimilan]

+1

While we're at it we should decide whether it's a good convention that traits start with Type as do TypeOrder, TypeArithmetic and TypeRangeStep in traits.jl. That convention isn't used anywhere else AFAIK, so the situation is inconsistent. Personally I don't really like these "Type" prefixes, as it's not clear what they mean.

[JeffBezanson]

Those names sound backwards to me; I'd expect OrderType or OrderStyle (to go with IndexStyle). But less urgent.