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/fullstack_hello_world.rs

@@ -0,0 +1,24 @@
+//! A simple example using Dioxus Fullstack to call a server action.
+//!
+//! the `get`, `post`, `put`, `delete`, etc macros are used to define server actions that can be
+//! called from the client. The action can take arguments and return a value, and the client
+//! will automatically serialize and deserialize the data.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(|| {
+        let mut message = use_action(get_message);
+
+        rsx! {
+            h1 { "Server says: "}
+            pre { "{message:?}"}
+            button { onclick: move |_| message.call("world".into(), 30), "Click me!" }
+        }
+    });
+}
+
+#[get("/api/{name}/?age")]
+async fn get_message(name: String, age: i32) -> Result<String> {
+    Ok(format!("Hello {}, you are {} years old!", name, age))
+}