fix(types): fix package.json exports for node16

[aloisklink]

When using TypeScript's new nodenext/node16 module setting, and using the new exports field in the package.json file, TypeScript no longer looks at the root types field for looking for type declarations.

Instead, you also need to add a types field within the exports field. The old types field should be kept for compatibility with older TypeScript versions.

See TypeScript docs on ECMAScript Modules in Node.js.

Example (copied from TypeScript docs) at https://www.typescriptlang.org/docs/handbook/esm-node.html#packagejson-exports-imports-and-self-referencing:

// package.json
{
    "name": "my-package",
    "type": "module",
    "exports": {
        ".": {
            // Entry-point for TypeScript resolution - must occur first!
            "types": "./types/index.d.ts",
            // Entry-point for `import "my-package"` in ESM
            "import": "./esm/index.js",
            // Entry-point for `require("my-package") in CJS
            "require": "./commonjs/index.cjs",
        },
    },
    // CJS fall-back for older versions of Node.js
    "main": "./commonjs/index.cjs",
    // Fall-back for older versions of TypeScript
    "types": "./types/index.d.ts"
}