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/03-assets-styling/dynamic_assets.rs

@@ -0,0 +1,31 @@
+//! This example shows how to load in custom assets with the use_asset_handler hook.
+//!
+//! This hook is currently only available on desktop and allows you to intercept any request made by the webview
+//! and respond with your own data. You could use this to load in custom videos, streams, stylesheets, images,
+//! or any asset that isn't known at compile time.
+
+use dioxus::desktop::{use_asset_handler, wry::http::Response};
+use dioxus::prelude::*;
+
+const STYLE: Asset = asset!("/examples/assets/custom_assets.css");
+
+fn main() {
+    dioxus::LaunchBuilder::desktop().launch(app);
+}
+
+fn app() -> Element {
+    use_asset_handler("logos", |request, response| {
+        // We get the original path - make sure you handle that!
+        if request.uri().path() != "/logos/logo.png" {
+            return;
+        }
+
+        response.respond(Response::new(include_bytes!("../assets/logo.png").to_vec()));
+    });
+
+    rsx! {
+        Stylesheet { href: STYLE }
+        h1 { "Dynamic Assets" }
+        img { src: "/logos/logo.png" }
+    }
+}