This CL fixes WebSnapshotDeserializer::DeserializeContexts(), so that
the new FunctionContext is allocated after the ScopeInfo is set up.

Bug: v8:11525, v8:11706
Change-Id: Idb14c0fa5b5d51827e9f208f54c82a94535343a4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2953292
Commit-Queue: Vicky Kontoura <vkont@google.com>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75099}