feat: add support for options.dereference.onDereference

[bcherny]

This callback is needed for https://github.com/bcherny/json-schema-to-typescript/pull/453, in order to more intelligently emit TypeScript types from JSON Schemas. Specifically, this change lets us use referenced names for type names, which results in more intuitive and human-readable types. I've implemented it as a generic hook for json-schema-ref-parser.