Allow to provide externs for inclusion in info.json
Do not process file type doclets
Build types only for olx.* symbols from externs
Dereference typedef
Prepend 'var ' for root symbols
Define constructor before its members
Keep track of all symbols

This avoids that we add parent namespaces of symbols that were already
added because they have their own definition in the externs.
Use {*} instead of {goog.*} types in externs file