Add back ReadableStream.getIterator and deprecate

Editor assessment

Add back ReadableStream.getIterator and deprecate states both actions precisely: the method is restored and simultaneously marked deprecated, which tells readers the compatibility intent. The op_crate/fetch scope is misspelled relative to the crate name - op_crates - which is a minor blemish, and the deprecation rationale is unstated. Still, the subject carries the essential change and hygiene is otherwise fine. Publishable. The restoration-plus-deprecation pairing communicates the compatibility intent clearly, though the reason the method needed deprecating in the first place is left unstated.