Add support to custom Webpack config

In lack of `input` flag webpack just targets the current directory

In some situations, e.g. 2 Nullstack in same env, the `declare module` is ran 2 times, this change limits their context

It still needs some trick to be recognized, though.

Some pkgs paths become obscure in some environments, e.g. `pnpm install`, `require.resolve` always finds wherever they are installed

Little webpack config improvements

✨ persistent hash

🚧 scriptless index

Little improvements at types

✨ add support for named environments

🔥 remove polyfill