These are similar to the Map/Set constructors when called with an array,
except that they are guaranteed to be side-effect free if called with
a packed array.

This will be useful in implementing structured clone which, as
specified in HTML, speaks in terms of the internal [[MapData]]
and [[SetData]] slots without going through the exposed iteration
ES semantics.

BUG=v8:3340
LOG=y

Review URL: https://codereview.chromium.org/1155893003

Cr-Commit-Position: refs/heads/master@{#28642}