Highlights:
- Record all imports and exports in the ModuleDescriptor.
- Remove ImportDeclaration; instead, introduce a new variable kind for imports.
- Set name on default exported anonymous functions.

Still to do: declaration of namespace imports.

BUG=v8:1569

Review-Url: https://codereview.chromium.org/2108193003
Cr-Commit-Position: refs/heads/master@{#37815}