[webcomponents] caretPositionFromPoint, elementFromPoint, and elementsFromPoint should respect shadow boundary (#313)

We should make these functions not return an element outside of its node tree.  Also, we need to define what happens when an element from another node tree is overlaying on top of the node tree in which these functions are called.  Do we return null in that case?  Or do we somehow by-pass those overlapping elements?  (The latter is going to be hard to implement).

I'm also inclined to say we may not want to include this in v1 given how undefined its behaviors are.

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/313