This removes the iteration protocol from the parser entirely, and opens
up future possibilities for more bytecodes implementing the various
functions of the protocol.

Change-Id: I316b8a92434d3b5f47927408a235ddaecd65d5bb
Reviewed-on: https://chromium-review.googlesource.com/c/1403125
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58795}