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/desktop/src/main.rs

@@ -0,0 +1,43 @@
+#![allow(non_snake_case)]
+use dioxus::prelude::*;
+
+fn main() {
+    // Make sure to set the url of the server where server functions are hosted - they aren't always at localhost
+    #[cfg(not(feature = "server"))]
+    dioxus::fullstack::set_server_url("http://127.0.0.1:8080");
+
+    dioxus::launch(app);
+}
+
+pub fn app() -> Element {
+    let mut count = use_signal(|| 0);
+    let mut text = use_signal(|| "...".to_string());
+
+    rsx! {
+        h1 { "High-Five counter: {count}" }
+        button { onclick: move |_| count += 1, "Up high!" }
+        button { onclick: move |_| count -= 1, "Down low!" }
+        button {
+            onclick: move |_| async move {
+                let data = get_server_data().await?;
+                println!("Client received: {}", data);
+                text.set(data.clone());
+                post_server_data(data).await?;
+                Ok(())
+            },
+            "Run a server function"
+        }
+        "Server said: {text}"
+    }
+}
+
+#[post("/api/data")]
+async fn post_server_data(data: String) -> ServerFnResult {
+    println!("Server received: {}", data);
+    Ok(())
+}
+
+#[get("/api/data")]
+async fn get_server_data() -> ServerFnResult<String> {
+    Ok("Hello from the server!".to_string())
+}