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/01-app-demos/counters.rs

@@ -0,0 +1,54 @@
+//! A simple counters example that stores a list of items in a vec and then iterates over them.
+
+use dioxus::prelude::*;
+
+const STYLE: Asset = asset!("/examples/assets/counter.css");
+
+fn main() {
+    dioxus::launch(app);
+}
+
+fn app() -> Element {
+    // Store the counters in a signal
+    let mut counters = use_signal(|| vec![0, 0, 0]);
+
+    // Whenever the counters change, sum them up
+    let sum = use_memo(move || counters.read().iter().copied().sum::<i32>());
+
+    rsx! {
+        Stylesheet { href: STYLE }
+
+        div { id: "controls",
+            button { onclick: move |_| counters.write().push(0), "Add counter" }
+            button { onclick: move |_| { counters.write().pop(); }, "Remove counter" }
+        }
+
+        h3 { "Total: {sum}" }
+
+        // Calling `iter` on a Signal<Vec<>> gives you a GenerationalRef to each entry in the vec
+        // We enumerate to get the idx of each counter, which we use later to modify the vec
+        for (i, counter) in counters.iter().enumerate() {
+            // We need a key to uniquely identify each counter. You really shouldn't be using the index, so we're using
+            // the counter value itself.
+            //
+            // If we used the index, and a counter is removed, dioxus would need to re-write the contents of all following
+            // counters instead of simply removing the one that was removed
+            //
+            // You should use a stable identifier for the key, like a unique id or the value of the counter itself
+            li { key: "{i}",
+                button { onclick: move |_| counters.write()[i] -= 1, "-1" }
+                input {
+                    r#type: "number",
+                    value: "{counter}",
+                    oninput: move |e| {
+                        if let Ok(value) = e.parsed() {
+                            counters.write()[i] = value;
+                        }
+                    }
+                }
+                button { onclick: move |_| counters.write()[i] += 1, "+1" }
+                button { onclick: move |_| { counters.write().remove(i); }, "x" }
+            }
+        }
+    }
+}