Better single fetch support for explicit loader/action return types

[aaronadamsCA]

We always define explicit return types, and single fetch is making this a bit tougher than it needs to be on our loaders and actions.

With json() deprecated in v2.14.0, we're updating our remaining actions to return plain objects where possible, and data() where necessary.

Unfortunately this means TypedResponse is out, and since DataWithResponseInit has not stabilized and is not re-exported by the Remix server runtime packages, for now we have to make it ourselves:

type DataWithResponseInit<T> = ReturnType<typeof data<T>>;

An official solution would be great.

Just re-exporting DataWithResponseInit would be fine, but even better would be something like SerializeTo<T> (as a counterpart to SerializeFrom<T>) that works whether you return a POJO or data().