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/ssr-only/src/main.rs

@@ -0,0 +1,59 @@
+//! This example showcases how to use Fullstack in a server-side rendering only context.
+//!
+//! This means we have no client-side bundle at all, and *everything* is rendered on the server.
+//! You can still use signals, resources, etc, but they won't be reactive on the client.
+//!
+//! This is useful for static site generation, or if you want to use Dioxus Fullstack as a server-side
+//! framework without the `rsx! {}` markup.
+//!
+//! To run this example, simply run `cargo run --package ssr-only` and navigate to `http://localhost:8080`.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(|| rsx! { Router::<Route> { } });
+}
+
+#[derive(Routable, Clone, Debug, PartialEq)]
+enum Route {
+    #[route("/")]
+    Home,
+
+    #[route("/post/:id")]
+    Post { id: u32 },
+}
+
+#[component]
+fn Home() -> Element {
+    rsx! {
+        h1 { "home"  }
+        ul {
+            li { a { href: "/post/1", "Post 1" } }
+            li { a { href: "/post/2", "Post 2" } }
+            li { a { href: "/post/3", "Post 3 (404)" } }
+        }
+    }
+}
+
+#[component]
+fn Post(id: u32) -> Element {
+    // You can return `HttpError` to return a specific HTTP status code and message.
+    // `404 Not Found` will cause the server to return a 404 status code.
+    //
+    // `use_loader` will suspend the server-side rendering until the future resolves.
+    let post_data = use_loader(move || get_post(id))?;
+
+    rsx! {
+        h1 { "Post {id}" }
+        p { "{post_data}" }
+    }
+}
+
+#[get("/api/post/{id}")]
+async fn get_post(id: u32) -> Result<String, HttpError> {
+    match id {
+        1 => Ok("first post".to_string()),
+        2 => Ok("second post".to_string()),
+        _ => HttpError::not_found("Post not found")?,
+    }
+}