Instead of storing both the {NativeModule} and the {WasmModule} in a
{Managed} object, just store the {WasmModule} in the {NativeModule}
directly. This fixes crashes that happen if the {Managed<WasmModule>}
dies before the {Managed<NativeModule>}.

R=mstarzinger@chromium.org

Bug: chromium:854794, v8:7879, v8:7889
Change-Id: I6b11729943fe7a03d225138782655ee5dafd26a6
Reviewed-on: https://chromium-review.googlesource.com/1118171
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54090}