This makes js-to-wasm wrappers module-independent, so that we can
eventually share them isolate-wide.

R=mstarzinger@chromium.org

Bug: chromium:862123
Change-Id: I3d9571cf247b95330ffb17f41901278a5dfacca0
Reviewed-on: https://chromium-review.googlesource.com/1131187
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54363}