With top-level await, when Evaluate is performed on an already-evaluated
synthetic module, Module::InnerEvaluate returns undefined.  This breaks
top-level await's assumption that the returned value is always a
promise.

In order to make SyntheticModule's behavior consistent with
SourceTextModule, the top_level_capability field is moved up to Module
and SyntheticModule::Evaluate places the promise returned from the
host's evaluation steps in that field.  Now SourceTextModule and
SyntheticModule can share the same code to handle the case where the
module is either kErrored or kEvaluated, so the code for this
is moved up to Module.

Thus, SyntheticModule is now guaranteed to return the
promise from the evaluation steps even on subsequent Evaluate() calls.

Unfortunately Node hasn't yet updated their EvaluationStepsCallback
to return a Promise, so we can't yet assume that the returned value
is a Promise without breaking Node.  So, this change also adds a clause
to check for this condition and create a new resolved Promise if one
was not provided by the callback steps.  This could eventually be
removed once Node's callback steps are updated for top-level await.

Change-Id: I2d6ae918abfeba9e3a757838502d4df92946edaa
Bug: v8:11398
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2673794Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dan Clark <daniec@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#72629}