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.

packages/fullstack/src/payloads/form.rs

@@ -0,0 +1,12 @@
+use super::*;
+
+pub use axum::extract::Form;
+
+impl<T> IntoRequest for Form<T>
+where
+    T: Serialize + 'static,
+{
+    fn into_request(self, req: ClientRequest) -> impl Future<Output = ClientResult> + 'static {
+        async move { req.send_form(&self.0).await }
+    }
+}