Currently we have things like like in the generated externs file (types.js):
/**
* @type {ol.control.AttributionOptions|undefined}
*/
olx.control.DefaultsOptionsExtern.prototype.attributionOptions;
It doesn't make sense to have external object properties whose types are
internal (ol.control.AttributionOptions in the above example).
With this commit, the generate-exports.py script generates this:
/**
* @type {olx.control.AttributionOptionsExtern|undefined}
*/
olx.control.DefaultsOptionsExtern.prototype.attributionOptions;