[webcomponents] Rename createShadowRoot to attachShadow (#129)

Given that chrome already shipped `createShadowRoot` and it's incompatible with the syntax we decided on at our April meeting, we need a new, possibly better name for the same. @rniwa, @hober, and @othermaciej and I briefly discussed this and came up with  `attachShadow`.


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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/129