Fix cycles during emission (fix #376, fix #323)

[bcherny]

WARNING: This is a breaking change, that changes names for some emitted types. It will require a major version bump.

Context

The problem: when emitting TS, we can run into a cycle when the emitted AST:

1. References a schema
2. That schema does not have a name
3. That schema references something (itself, or another schema) that eventually references that same schema

The approach in this PR

This PR has 2 parts:

1. An upstream PR to json-schema-ref-parser (forked for now, will upstream later) to add an onDereference hook that we can use to grab the original $ref path for dereferenced schemas.
2. This PR, which takes advantage of original $refs to more correctly name emitted types.

(2) is something I've wanted to do for a while. It gives us more correct behavior (which we only approximated before), and more fully deals with cyclical references.

Alternative solutions considered

• Always generate standalone names for interfaces & arrays. This fully avoids cycles, but loses the elegance of emitting inline objects for simple unnamed schemas.
• When we detect a cycle, look behind to add a standalone name to the closest thing that needs it
• When we generate a type, look ahead to see if there's a cycle, and if so, generate a standalone name for the given type