Closure modules can largely be treated the same as commonjs modules (notably
resolving type references in comments against the module's internal types).
Record a module's exported type as an alias for that type's compiler-defined
reference name.
When we can resolve a symbol to its parent type but not an individual property,
link to the parent type's page, but omit the fragment (since it's not a
recognized property).
Mangle extern module IDs so we can render the names properly in generated
documentation.