collection: remove static factory methods from contract

[Lctrs]

Those static factory methods are tied to how the default implementation works, and makes it hard to provide an alternative implementation.

For exemple, I have some use cases where I already know the number of items in the iterable, and I would like to pass it to the alternative implementation to avoid calling iterator_count()

[drupol]

Hi,

Thanks for your contribution.

Changing stuff in the interface is often a backward incompatible change.

I'm usually a bit reluctant to include this change but in this particular case, it's fine because those methods are basically the static constructors and we will never call them from the interface (CollectionInterface::fromIterable).

Give me a bit of time to think about it.

In the meantime, could you please provide a code example of what you're trying to do?

Thanks.

[drupol]

After our interesting discussion on Slack, we came to the conclusion that this PR is definitely valid.

Thanks!

[Lctrs]

Thank you !