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/hello_world.rs

@@ -0,0 +1,22 @@
+//! The simplest example of a Dioxus app.
+//!
+//! In this example we:
+//! - import a number of important items from the prelude (launch, Element, rsx, div, etc.)
+//! - define a main function that calls the launch function with our app function
+//! - define an app function that returns a div element with the text "Hello, world!"
+//!
+//! The `launch` function is the entry point for all Dioxus apps. It takes a function that returns an Element. This function
+//! calls "launch" on the currently-configured renderer you have. So if the `web` feature is enabled, it will launch a web
+//! app, and if the `desktop` feature is enabled, it will launch a desktop app.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    rsx! {
+        div { "Hello, world!" }
+    }
+}