Add support for converting constant size arrays into tuples

[orhanhenrik]

Fixes #1884

This PR implements a new option --useTuples which converts constant size arrays into constant size typescript arrays.

I'm not too happy with how the logic ended up partially in handlebars and partially in typescript, so if you have any suggestions for how I could make this work better with the project's code structure I would appreciate that! The problem I was facing was that I didn't have access to any options inside getModel without having to pass the useTuples option throughout the whole program.

Example

MyModel: {
  type: 'object',
  properties: {
    coordinates: {
      type: 'array',
      items: {
        type: 'number',
      },
      minItems: 2,
      maxItems: 2,
    },
  },
},

Without --useTuples

export type MyModel = {
  coordinates: Array<number>;
}

With --useTuples

export type MyModel = {
  coordinates: [number, number];
}

[nicholaschiang]

+1

[orhanhenrik]

Works in the maintained fork of this library https://github.com/hey-api/openapi-ts