This moves JavaScript source files that are bundled with V8 into a
separate directory. The goal is to improve code readability and also
being able to formalize ideal reviewers by subsequently adding the
OWNERS file. These files almost exclusively contain implementations
of methods fully specified by ES6.

Note that files in the "debug" directory as well as the "d8.js" file
aren't affected by this change.

R=rossberg@chromium.org

Review URL: https://codereview.chromium.org/1398733002

Cr-Commit-Position: refs/heads/master@{#31230}