Position of Identifiers sometimes covers other tokens

[dennwc]

There are some cases where positional information in identifiers covers the whole parameter declaration.

Here is one of the failing cases:
https://github.com/bblfsh/javascript-driver/blob/master/fixtures/ext_typedecl.js#L9

const packageToBabelConfig = makeWeakCache(
  (file: ConfigFile): ConfigFile | null => {

In the AST positional info of the file identifier covers file: ConfigFile for some reason. See TODO.