Copy input ArrayBuffers

[a-sully]

Fixes #566

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[inexorabletash]

My reading of "get a copy of the bytes" is that if the buffer is detached then an empty byte sequence is returned but we don't explicitly throw.

Per #351 (and my #723) we want to error if transferring a detached buffer (which will still be used for output buffers). Should we error for detached input buffers too?

I think that just requires adding If |view| is [=BufferSource/detached=], then throw a {{TypeError}}. to the steps.

(I think we'd still end up throwing in most cases since the subsequent size check will fail. Although if allow 0 size dimensions (#391) there would be a weird case where it might slip through that check. Harmless, but weird?)