This is the seventh CL in a series to improve our module decoder tests
and make them more readable.

R=titzer@chromium.org

Bug: v8:8238
Change-Id: Ib8bd2cc3f2fdb23b39511657a4af99f6fa781172
Reviewed-on: https://chromium-review.googlesource.com/c/1286346
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56737}