This migrates harness adjustments, to be loaded after mjsunit.js on
fuzzers for correctness fuzzing.

This is the first step adding deeper pretty printing. Other
adjustments will be added in follow ups.

Bug: chromium:813833
Change-Id: I51168a31e733d54808cb8853a1c90e897acf3791
Reviewed-on: https://chromium-review.googlesource.com/930565
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51481}