This change is a partial implementation of Synthetic Module Record as specified here:
https://heycam.github.io/webidl/#synthetic-module-records

This includes:
- Introduce SyntheticModule class inheriting from Module.
- Extend v8::Module interface in v8.h to include Synthetic Module APIs, with corresponding
  implementations in api.cc.
- Provide SyntheticModule implementations of PrepareInstantiate, FinishInstantiate, and SetExport.
- Provide cctest unit tests for the implementations in the preceding item.

We will follow up with further submissions to implement the remaining members of
SyntheticModule (ResolveExport and Evaluate).

Bug: v8:9292
Change-Id: I25b1b695b5d1c3004677cd685f0dfd95283438fa
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1626829
Commit-Queue: Dan Clark <daniec@microsoft.com>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62433}