Consider for migrate to ESM-only package

`parse5` v8 has migrate to ESM-only package, so i think if we should.
But before migrating, we MUST ONLY support Node.js with the minimum version is `20`.
Because on that version, CommonJS can import an ESM file.

> [!NOTE]
> Node.js with version under `20` is deprecated.

```js
// This is works
const esm = require("./esm.mjs");
```

This will reduce half of the package size. Agree @fb55?