This changes all tools to use ES6 modules and proper imports.

Step 1: Add converted .mjs files (*this CL*)
Step 2: Update node-ci build to use new .mjs files
Step 3: Remove outdated .js files

Bug: v8:10667, v8:10933
Change-Id: I3e92e66f896d8a9cacaf6d421f8d2c86fb3bc444
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2431045
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Sathya Gunasekaran  <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70163}