fix(js-component-bindgen): treat undefined as none when lowering options

[GamePad64]

_lowerFlatOption mapped only JS null to the option none case, but jco's own generated TypeScript types model option<T> none as T | undefined. A value of undefined was therefore lowered as some(undefined); when T contains an own<resource>, _lowerFlatOwn then throws missing resource and aborts the task.

This surfaced with wasi:http p3 response.consume-body, whose trailers future is typed Result<Trailers | undefined, ErrorCode>: an empty-trailers Ok(None) ({ tag: 'ok', val: undefined }) crashed lowering at body completion, leaving the enclosing streaming result's .next() unresolved.

Widen the none check to accept undefined, consistent with the generated types.

[vados-cosmonic]

LGTM 🚀

Thanks for this fix @GamePad64 !

I really think that we should be leaning towards null here other than undefined, but the current type representation documentation it looks like we really do use undefined.

This is probably something left for a breaking change in Jco for the future -- null is an explicit value (that is none-ish) whereas undefined overlaps with a completely missing option, which makes null seem like the better representation here (there are some benefits like when making objects for record values)... That's a conversation for a different time, I guess.