[webcomponents] importNode and adoptNode should throw with passed a ShadowRoot (#125)

Given that cloneNode throws with a shadow root, importNode should also throw because one of the steps in the import algorithm it to clone the node. Also, adoptNode should also throw because the host and shadow root shouldn't have different node documents.

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/125