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/01-app-demos/hotdog/src/main.rs

@@ -0,0 +1,29 @@
+mod backend;
+mod frontend;
+
+use dioxus::prelude::*;
+use frontend::*;
+
+#[derive(Routable, PartialEq, Clone)]
+enum Route {
+    #[layout(NavBar)]
+    #[route("/")]
+    DogView,
+
+    #[route("/favorites")]
+    Favorites,
+}
+
+fn main() {
+    #[cfg(not(feature = "server"))]
+    dioxus::fullstack::set_server_url("https://hot-dog.fly.dev");
+
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    rsx! {
+        Stylesheet { href: asset!("/assets/main.css") }
+        Router::<Route> {}
+    }
+}