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/08-apis/eval.rs

@@ -0,0 +1,47 @@
+//! This example shows how to use the `eval` function to run JavaScript code in the webview.
+//!
+//! Eval will only work with renderers that support javascript - so currently only the web and desktop/mobile renderers
+//! that use a webview. Native renderers will throw "unsupported" errors when calling `eval`.
+
+use async_std::task::sleep;
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    // Create a future that will resolve once the javascript has been successfully executed.
+    let future = use_resource(move || async move {
+        // Wait a little bit just to give the appearance of a loading screen
+        sleep(std::time::Duration::from_secs(1)).await;
+
+        // The `eval` is available in the prelude - and simply takes a block of JS.
+        // Dioxus' eval is interesting since it allows sending messages to and from the JS code using the `await dioxus.recv()`
+        // builtin function. This allows you to create a two-way communication channel between Rust and JS.
+        let mut eval = document::eval(
+            r#"
+                dioxus.send("Hi from JS!");
+                let msg = await dioxus.recv();
+                console.log(msg);
+                return "hi from JS!";
+            "#,
+        );
+
+        // Send a message to the JS code.
+        eval.send("Hi from Rust!").unwrap();
+
+        // Our line on the JS side will log the message and then return "hello world".
+        let res: String = eval.recv().await.unwrap();
+
+        // This will print "Hi from JS!" and "Hi from Rust!".
+        println!("{:?}", eval.await);
+
+        res
+    });
+
+    match future.value().as_ref() {
+        Some(v) => rsx!( p { "{v}" } ),
+        _ => rsx!( p { "waiting.." } ),
+    }
+}