First step towards making arguments and rest parameters optimizable by
splitting the allocations for the actual object and the elements. The
object allocations can already be escape analyzed this way, the elements
would need special support in the deoptimizer and the escape analysis,
but that can be done as a second separate step.

R=jarin@chromium.org
BUG=v8:5726

Review-Url: https://codereview.chromium.org/2557283002
Cr-Commit-Position: refs/heads/master@{#41573}