deps: backport 200315c from V8 upstream (v4.x)
Original commit message:
Make AstRawString deduplication encoding-agnostic.
R=jkummerow@chromium.org BUG=v8:4450 LOG=N
Review URL: https://codereview.chromium.org/1411103006
Cr-Commit-Position: refs/heads/master@{#31624}
cc @nodejs/v8 @nodejs/lts