fix: correct types for node16 resolution

[bradzacher]

Fixes #46

1. Adds a rollup step to generate a .d.cts file for the .cjs bundle
2. Fixes the unnecessary type cycle in lib files

Test plan

npm pack and upload the tarball to arethetypeswrong:

Regarding the "masquerading" issue reported - it shouldn't cause a problem technically: arethetypeswrong/arethetypeswrong.github.io#21
Ideally the output files should be .mjs/.d.mts to be explicit, but it is okay without it (it's more of a pedantic report from my understanding).

I tested this works as expected by continuing the exmaple in #46:

$ echo "import * as foo from 'eslint-visitor-keys';\nexport default foo.shoulderror;" > test2.mts
$ echo "import * as foo from 'eslint-visitor-keys';\nexport default foo.shoulderror;" > test3.cts
$ echo "import foo = require('eslint-visitor-keys');\nexport default foo.shoulderror;" > test4.cts
$ npx tsc -b ./tsconfig.json

And it worked as expected and correctly resolved the types.

[mdjermanovic]

eslint-visitor-keys.d.cts

type VisitorKeys$1 = {
    readonly [type: string]: readonly string[];
};
/**
 * @typedef {{ readonly [type: string]: ReadonlyArray<string> }} VisitorKeys
 */
/**
 * @type {VisitorKeys}
 */
declare const KEYS: VisitorKeys$1;

/**
 * Get visitor keys of a given node.
 * @param {object} node The AST node to get keys.
 * @returns {readonly string[]} Visitor keys of the node.
 */
declare function getKeys(node: object): readonly string[];
/**
 * Make the union set with `KEYS` and given keys.
 * @param {VisitorKeys} additionalKeys The additional keys.
 * @returns {VisitorKeys} The union set.
 */
declare function unionWith(additionalKeys: VisitorKeys): VisitorKeys;

type VisitorKeys = VisitorKeys$1;

export { KEYS, VisitorKeys, getKeys, unionWith };

exported KEYS will be of type VisitorKeys$1 instead of VisitorKeys. Is that okay?

[bradzacher]

exported KEYS will be of type VisitorKeys$1 instead of VisitorKeys. Is that okay

Yes - the names are not required to be the same - the name is just an alias.
The types are resolved to their actual representation before they are checked by TS.

[mdjermanovic]

LGTM, thanks!

Leaving open for others to review.

[snitin315]

LGTM. Thanks for contributing 🚀