Add a new mode to generate-bytecode-expectations to be used in a coming
test that tests that the bytecode expectations generated by
--rebaseline match the current state.

Change-Id: Ic03787cd853f9bf7d9b4412f96a767036c848c61
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1708477
Auto-Submit: Dan Elphick <delphick@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62825}