- Suspender.suspendOnReturnedPromise expects a function with type
[ti*]->[externref] and returns a function with the same type.
- Suspender.returnPromiseOnSuspend expects a function with type
[ti*]->[to] and returns a function with type [ti*]->[externref].

Changes:
- Check the wrapped function's return types
- Skip type checking of return types when importing a wrapper (and
assert that the return type is externref)
- Add special case for WebAssembly.Function.type of a
WasmExportedFunction: it currently returns the signature declared by
the module. Change the return type to externref if this is a
stack-switching export.

Bug: v8:12191
Change-Id: I6619c306e9613825ad1b021cb3400d73cd684656
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3435190Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78973}