Schema without a type should be "any" or "unknown" instead of a generic map type

[pbzdyl]

According to the OpenAPI spec, when a schema is defined without a type it is the equivalent of:

      anyOf:
        - type: string
        - type: number
        - type: integer
        - type: boolean
        - type: array
          items: {}
        - type: object

but openapi-typescript uses object type as the default and generates { [key: string]: unknown }. Instead it should generate just unknown.

[drwpow]

I’m in favor of this change. I’m thinking that this along with #554 should result in a new major (breaking) version bump that makes these type changes. I have held off on these because it would be just disruptive enough to people that I’d want them to be able to delay switching. But I agree that long-term, following the spec more closely is best.

[pbzdyl]

Thank you so much @drwpow!