This shares JS-to-Wasm wrapper code across instances belonging to the
same module object. We no longer need to copy the wrappers since they
are by now independent of the concrete instance.

R=titzer@chromium.org
BUG=v8:7424

Change-Id: I54188eae6378e53cc274cd19f8e652ffdba72ee5
Reviewed-on: https://chromium-review.googlesource.com/1049607
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53058}