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/full_request_access.rs

@@ -0,0 +1,37 @@
+//! This example shows how to get access to the full axum request in a handler.
+//!
+//! The extra arguments in the `post` macro are passed to the handler function, but not exposed
+//! to the client. This means we can still call the endpoint from the client, but have full access
+//! to the request on the server.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    let mut file_id = use_action(full_request);
+
+    rsx! {
+        div { "Access to full axum request" }
+        button { onclick: move |_| file_id.call(), "Upload file" }
+    }
+}
+
+/// Example of accessing the full axum request in a handler
+///
+/// The `request: axum_core::extract::Request` argument is placed in the handler function, but not
+/// exposed to the client.
+#[post("/api/full_request_access", request: axum_core::extract::Request)]
+async fn full_request() -> Result<()> {
+    let headers = request.headers();
+
+    if headers.contains_key("x-api-key") {
+        println!("API key found");
+    } else {
+        println!("No API key found");
+    }
+
+    Ok(())
+}