Kotlin: Support JVM class hierarchy when resolving common ancestors

[kdubb]

If a union of types (or equivalent) is known at generation time to the JVM (i.e. can be loaded via class loader), then the JVM hierarchy of that type should be considered when resolving the common ancestor of the types.

For example, given the following RAML:

types:
  Int:
    type: number
    format: int32

  Float:
    type: number
    format: float

  Number: (Int | Float)

The common ancestor of Number should resolve to kotlin.Number.

Currently it resolves to kotlin.Any.