EncodeLike<Vec<T>> should be implemented for Iterators with wrapping structure

[gui1117]

Similarly to Ref structure we could introduce

struct Iter<I: Iterator<T>, T: Encode>(&I, Phantom<T>)

or maybe

struct Iter<I: Iterator<T>, T: EncodeLike<U>, U: Encode>(&I, Phantom<(T, U)>)

And then implement EncodeLike<Vec<U>> for it.

[gui1117]

I mean this can be helpful to achieve the constained of append_or_put in substrate.