The JS import returns a tagged value, not a value of the machine
representation that corresponds to the signature's return type, since it
hasn't been converted yet.

R=ahaas@chromium.org

Bug: v8:12191
Change-Id: I0783af85eed9c5d25347200540e3e4eee48edfd4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3464036Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#80213}