This adds support for lowering {JSCreateArguments} within outermost
frames of type {CreateArgumentsType::kMappedArguments}. It will hence
enable escape analysis to work with such objects and allow for further
optimization.

This also adds a new {NewMappedArgumentsElements} simplfied operator.
Note that escape analysis support for this new operator will be done as
a follow-up.

R=tebbi@chromium.org

Change-Id: I0e2fac25c654f796433f57b116964053b6b68635
Reviewed-on: https://chromium-review.googlesource.com/641454
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47761}