Suspense boundaries/pure HTML out of order streaming/anyhow like error handling

[ealmloff]

This PR improves context based suspense by bubbling suspense to the nearest suspense boundary.

This allows you to handle suspense at a single boundary which makes it easier to show an unified loading UI.

It uses the current extension trait to return early when a suspended resource is encountered, but this now returns an error instead of None to avoid issues when the suspense is handled manually in the component.

// Suspense context
#[component]
fn Parent() -> Element {
    rsx! {
        ErrorBoundary {
            handle_error: |err| rsx! { div { {err} } },
            Suspense {
                pending: |suspense| rsx! { div { {suspense} } },
                Doggo {}
            }
        }
    }
}

#[component]
fn Doggo() -> Element {
    let download_progress = use_signal(|| 0.);
    let mut fut = use_resource(move || async move { download_model(download_progress).await })
        .suspend()
        // You can optionally add a hint for the suspense boundary to render
        .show(move || rsx!("Downloading LLM... {download_progress}% done))?
        .throw()
        // You can optionally add a hint for the error boundary to render
        .show_with(|err| rsx!("hugging face is down 🙁: {err:?}"))?;

    todo!()
}

Breaking changes:

• This PR changes the Element type from Option to Result to make it easier to return errors early, and properly track the result of the component. Without this change, if you throw or suspend, handle it manually and then return None manually, dioxus will try to handle the suspense/error for you

Closes #1335

Stacked on top of #2226, #2437

[ealmloff]

Out of order SSR is working on the server. Still some work to do to make client side suspense work correctly. Out of order SSR without JS makes it possible stream updates while your WASM is still loading which should be nice for large wasm bundles

Screen.Recording.2024-05-21.at.12.15.45.PM.mov