This assigns dummy instance templates to all WebAssembly API functions
used as constructors. It hence avoids implicit receivers from having the
internal instance types. These objects would never be fully initialized
and causes heap iterations to stumble over these objects.

R=clemensh@chromium.org
BUG=v8:8003

Change-Id: I3c81d8dc3ae4a38e650b390a04170585cb31ec77
Reviewed-on: https://chromium-review.googlesource.com/1170685Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55037}