openapi 3.1 - support tuples

[chrisradek]

Open API 3.1 supports defining tuples via Json Schema prefixItems.

Given the following TypeSpec:

model Foo {
  tuple: [string, string];
}

We can emit an Open API 3.1 schema that looks like this:

Foo:
  type: object
  properties:
    tuple:
      type: array
      prefixItems:
        - type: string
        - type: string
  required:
    - tuple

This matches what our json schema emitter currently emits.

For reference, our Open API 3.0 emitter does not support emitting tuples due to the lack of prefixItems and instead outputs this:

Foo:
  type: object
  required:
    - tuple
  properties:
    tuple:
      type: array
      items: {}