`snippets` are not included in `package.json` `files`

[hgiesel]

🐛 Bug description

There are scenarios, where snippets are generated in a snippets directory inside of pkg, also see here.

🤔 Expected Behavior

Once snippets exist, I would expect to be included in the files part of package.json. Otherwise they're not shipped

👟 Steps to reproduce

Create a snippet, e.g. with #[wasm_bindgen(inline_js = #js_lit)] and watch it not being included when packaging.

🌍 Your environment

Include the relevant details of your environment.
wasm-pack version: latest
rustc version: latest