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

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