Add exports.*.types instead of @ts-self-types

[ai]

As I understand for JS files needs Deno a way to find .d.ts types without scanning file system. Right now we are using comments like /* @ts-self-types="./index.d.ts" */.

Adding these comments doesn’t look beautiful for me and for esthetic reasons I prefer to have something like:

{
  "name": "@sitnik/nanoid",
  "version": "5.1.0",
  "license": "MIT",
  "exports": {
    ".": {
      "types": "./index.d.ts",
      "default": "./index.js"
    }
  }
}