codify "platform" into resolution logic, server-fn/fullstack overhaul (#4596)

overhaul dioxus fullstack using a new implementation of server_fn

This PR is a complete rewrite of dioxus fullstack designed to improve compatibility with axum and to fix a number of compilation errors based on feature flag unification plumbing through macros.

examples/05-using-async/streams.rs

@@ -0,0 +1,37 @@
+//! Handle async streams using use_future and awaiting the next value.
+
+use async_std::task::sleep;
+use dioxus::prelude::*;
+use futures_util::{Stream, StreamExt, future, stream};
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    let mut count = use_signal(|| 10);
+
+    use_future(move || async move {
+        // Create the stream.
+        // This could be a network request, a file read, or any other async operation.
+        let mut stream = some_stream();
+
+        // Await the next value from the stream.
+        while let Some(second) = stream.next().await {
+            count.set(second);
+        }
+    });
+
+    rsx! {
+        h1 { "High-Five counter: {count}" }
+    }
+}
+
+fn some_stream() -> std::pin::Pin<Box<dyn Stream<Item = i32>>> {
+    Box::pin(
+        stream::once(future::ready(0)).chain(stream::iter(1..).then(|second| async move {
+            sleep(std::time::Duration::from_secs(1)).await;
+            second
+        })),
+    )
+}