This removes the dependency on Lua for running gcmole, and Python's
expressiveness lets us clean up the code a bit, including getting rid
of global variables, embedding the multiprocessing (removing the need
for a separate `parallel.py`), and using difflib for printing the test
expectation diff.

Bug: v8:11169, v8:8590, chromium:1097212
Change-Id: If0ab5ea6f764864855d73cd0ba63cb37c1823955
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2543927
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71253}