REF: delegate more IntervalIndex methods
cc @jschendel is the usage of _simple_new instead of _shallow_copy `take` important?  Should it always be the case that `idx.close == idx._data.closed`?
> is the usage of `_simple_new` instead of `_shallow_copy` in `take` important?

I don't think so.

> should it always be the case that `idx.closed == idx._data.closed`?

Yes. thanks @jbrockmendel 