The FunctionLiteral returned from the parser for modules now has a MODULE_SCOPE,
instead of associating the module scope with a Block inside it. This makes
it easy to get at the ModuleDescriptor from the caller of Parse(), so I've added
a basic test that pokes at the scope and the descriptor. Expect more tests
in this vein.

BUG=v8:1569
LOG=n

Review URL: https://codereview.chromium.org/953983002

Cr-Commit-Position: refs/heads/master@{#26836}