Refactor the ArrayIteratorPrototypeNext CSA builtin to handle the
JSArray element access in a dedicated helper macro, very similar
to how it's done for JSTypedArray's. Also add support for dictionary
elements to this helper macro using the existing dictionary access
logic in the CodeStubAssembler.

This improves the readability of the builtin significantly and the
performance of iterating arrays with dictionary elements goes up by
a factor of ~3.5x.

Bug: v8:8015, v8:8070
Change-Id: Ibfee760ea1e4bc0fffb42b232fb1d097b706bd1f
Reviewed-on: https://chromium-review.googlesource.com/1183305Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55283}