Resolve with array instead of SplObjectStorage (AdapterInterface::ls(), Node\DirectoryInterface::lsRecursive(), Node\NodeInterface::copy, ObjectStreamSink::promise())

[ghost]

As discussed in the comments of #57 - this PR changes ObjectStreamSink::promise to resolve with an array, instead of an unexpected SplObjectStorage.

[clue]

Thanks for filing this PR, I agree that using an array makes much more sense here 👍

It looks like this is only a minor change in the internal APIs, but this seems to have a bigger impact on the user-facing APIs. I'm fine with this change, but can we get a list of affected functions for our upgrade guides and ensure they are all covered? Accordingly, docs and examples might have to be updated, e.g. https://github.com/reactphp/filesystem#list-contents.

[ghost]

Affected by this change are the following methods:

• AdapterInterface::ls (needs to be upgraded by users due to promises anyway)
• Node\NodeInterface::copy (Directory, File and Link node instances)
• Node\DirectoryInterface::lsRecursive (Directory node instances)

[clue]

@CharlotteDunois Thanks for the quick update, LGTM! 👍