[streams] ReadableStream.getReader name is a bit misleading (#308)

getReader name is a little bit counter-intuitive to me.
This method is really a constructor.
Its name seems to imply that it could return the same object if called several times on the same stream.
Why not simply calling it ReadableStream.createReader?

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Reply to this email directly or view it on GitHub:
https://github.com/whatwg/streams/issues/308