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/backgrounded_futures.rs

@@ -0,0 +1,65 @@
+//! Backgrounded futures example
+//!
+//! This showcases how use_future, use_memo, and use_effect will stop running if the component returns early.
+//! Generally you should avoid using early returns around hooks since most hooks are not properly designed to
+//! handle early returns. However, use_future *does* pause the future when the component returns early, and so
+//! hooks that build on top of it like use_memo and use_effect will also pause.
+//!
+//! This example is more of a demonstration of the behavior than a practical use case, but it's still interesting to see.
+
+use async_std::task::sleep;
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    let mut show_child = use_signal(|| true);
+    let mut count = use_signal(|| 0);
+
+    let child = use_memo(move || {
+        rsx! {
+            Child { count }
+        }
+    });
+
+    rsx! {
+        // Some toggle/controls to show the child or increment the count
+        button { onclick: move |_| show_child.toggle(), "Toggle child" }
+        button { onclick: move |_| count += 1, "Increment count" }
+
+        if show_child() {
+            {child()}
+        }
+    }
+}
+
+#[component]
+fn Child(count: WriteSignal<i32>) -> Element {
+    let mut early_return = use_signal(|| false);
+
+    let early = rsx! {
+        button { onclick: move |_| early_return.toggle(), "Toggle {early_return} early return" }
+    };
+
+    if early_return() {
+        return early;
+    }
+
+    use_future(move || async move {
+        loop {
+            sleep(std::time::Duration::from_millis(100)).await;
+            println!("Child")
+        }
+    });
+
+    use_effect(move || println!("Child count: {}", count()));
+
+    rsx! {
+        div {
+            "Child component"
+            {early}
+        }
+    }
+}