Set sideEffects to true if #[wasm_bindgen(start)] is present

[Flashs]

💡 Feature description

I'm currently working on a project using yew + webpack for the frontend.

I ran into a small issue where i have specified the start function with #[wasm_bindgen(start)] but the import got excluded from the bundled javascript file by webpack. This is because the package.json contains sideEffets : false and the library not being used otherwise. This isn't really a huge issue for me though and I'm not sure how easy or compicated it is to implement.

I just wanted to point it out, in case someone else faces the same issue.