The current implementation only supports arrays and proxies as
multi-return values in Wasm to JS calls. This adds support for any
iterable including generators, as specified by the multi-value proposal
(https://github.com/WebAssembly/multi-value/).

R=mstarzinger@chromium.org

Bug: v8:9492
Change-Id: I2c9be1f7e03824b1aabba525244e5b7f76a98f99
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1824938
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63996}