In addition to decoding them, we also have to evaluate the initializer
instructions when instantiating a module.
Drive-by fix: use "big-endian" encoding (prefix comes first) when
emitting initializers in the module builder.

Bug: v8:7748
Change-Id: Idfa0f5db298a8f6c6100fc09e1984e4a2e170e4a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2298004
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68866}