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/07-fullstack/custom_axum_serve.rs

@@ -0,0 +1,46 @@
+//! This example demonstrates how to use `dioxus::serve` with a custom Axum router.
+//!
+//! By default, `dioxus::launch` takes over the main thread and runs the Dioxus application.
+//! However, if you want to integrate Dioxus into an existing web server or use a custom router,
+//! you can use `dioxus::serve` to create a server that serves your Dioxus application alongside
+//! other routes.
+//!
+//! `dioxus::serve` sets up an async runtime, logging, hot-reloading, crash handling, and more.
+//! You can then use the `.serve_dioxus_application` method on your router to serve the Dioxus app.
+//!
+//! `dioxus::serve` is most useful for customizing the server setup, such as adding middleware,
+//! custom routes, or integrating with existing axum backend code.
+//!
+//! Note that `dioxus::serve` is accepts a Router from `axum`. Dioxus will use the IP and PORT
+//! environment variables to determine where to bind the server. To customize the port, use environment
+//! variables or a `.env` file.
+//!
+//! On other platforms (like desktop or mobile), you'll want to use `dioxus::launch` instead and then
+//! handle async loading of data through hooks like `use_future` or `use_resource` and give the user
+//! a loading state while data is being fetched.
+
+use dioxus::prelude::*;
+
+fn main() {
+    // On the client we just launch the app as normal.
+    #[cfg(not(feature = "server"))]
+    dioxus::launch(app);
+
+    // On the server, we can use `dioxus::serve` and `.serve_dioxus_application` to serve our app with routing.
+    // The `dioxus::server::router` function creates a new axum Router with the necessary routes to serve the Dioxus app.
+    #[cfg(feature = "server")]
+    dioxus::serve(|| async move {
+        use dioxus::server::axum::routing::{get, post};
+
+        Ok(dioxus::server::router(app)
+            .route("/submit", post(|| async { "Form submitted!" }))
+            .route("/about", get(|| async { "About us" }))
+            .route("/contact", get(|| async { "Contact us" })))
+    });
+}
+
+fn app() -> Element {
+    rsx! {
+        div { "Hello from Dioxus!" }
+    }
+}