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/on_resize.rs

@@ -0,0 +1,27 @@
+//! Run a callback
+//!
+//! Whenever an Element is finally mounted to the Dom, its data is available to be read.
+//! These fields can typically only be read asynchronously, since various renderers need to release the main thread to
+//! perform layout and painting.
+
+use dioxus::prelude::*;
+use dioxus_elements::geometry::euclid::Size2D;
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    let mut dimensions = use_signal(Size2D::zero);
+
+    rsx!(
+        Stylesheet { href: asset!("/examples/assets/read_size.css") }
+        div {
+            width: "50%",
+            height: "50%",
+            background_color: "red",
+            onresize: move |evt| dimensions.set(evt.data().get_content_box_size().unwrap()),
+            "This element is {dimensions():?}"
+        }
+    )
+}