This adds test coverage for the encoding and decoding of s128 values as
part of an exception package. The encoding within an exception package
is not specified (and not observable), but the full bit-pattern needs to
survive an encoding/decoding round trip.

R=clemensb@chromium.org
TEST=mjsunit/wasm/exceptions-simd
BUG=v8:8091

Change-Id: I4cf6c1f00c64757512f66d068640a7e772eb0127
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1905769
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64932}