Use a Foreign pointer for the signature in the generic JS-to-Wasm wrapper.

Bug: v8:10701
Change-Id: I30d5894e8b8a48c258b7a6e003813c8403c1075e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2369178Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Eva Herencsárová <evih@google.com>
Cr-Commit-Position: refs/heads/master@{#69580}