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/08-apis/multiwindow.rs

@@ -0,0 +1,32 @@
+//! Multiwindow example
+//!
+//! This example shows how to implement a simple multiwindow application using dioxus.
+//! This works by spawning a new window when the user clicks a button. We have to build a new virtualdom which has its
+//! own context, root elements, etc.
+
+use dioxus::prelude::*;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    let onclick = move |_| {
+        dioxus::desktop::window().new_window(VirtualDom::new(popup), Default::default());
+    };
+
+    rsx! {
+        button { onclick, "New Window" }
+    }
+}
+
+fn popup() -> Element {
+    let mut count = use_signal(|| 0);
+    rsx! {
+        div {
+            h1 { "Popup Window" }
+            p { "Count: {count}" }
+            button { onclick: move |_| count += 1, "Increment" }
+        }
+    }
+}