Currently, the stack-switching import wrapper always suspends. Only
suspend if the returned value is a promise, otherwise just convert and
return the value back to wasm.

R=ahaas@chromium.org
CC=fgm@chromium.org

Bug: v8:12191
Change-Id: I26e7a3921aeae30fcce7f0ccc98d790a1a6f8c35
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3440655Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78980}