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.

packages/fullstack-core/src/document.rs

@@ -0,0 +1,57 @@
+//! On the client, we use the [`FullstackWebDocument`] implementation to render the head for any elements that were not rendered on the server.
+
+use dioxus_document::*;
+
+fn head_element_written_on_server() -> bool {
+    crate::transport::head_element_hydration_entry()
+        .get()
+        .ok()
+        .unwrap_or_default()
+}
+
+/// A document provider for fullstack web clients
+#[derive(Clone)]
+pub struct FullstackWebDocument<D> {
+    document: D,
+}
+
+impl<D> From<D> for FullstackWebDocument<D> {
+    fn from(document: D) -> Self {
+        Self { document }
+    }
+}
+
+impl<D: Document> Document for FullstackWebDocument<D> {
+    fn eval(&self, js: String) -> Eval {
+        self.document.eval(js)
+    }
+
+    /// Set the title of the document
+    fn set_title(&self, title: String) {
+        self.document.set_title(title);
+    }
+
+    /// Create a new meta tag in the head
+    fn create_meta(&self, props: MetaProps) {
+        self.document.create_meta(props);
+    }
+
+    /// Create a new script tag in the head
+    fn create_script(&self, props: ScriptProps) {
+        self.document.create_script(props);
+    }
+
+    /// Create a new style tag in the head
+    fn create_style(&self, props: StyleProps) {
+        self.document.create_style(props);
+    }
+
+    /// Create a new link tag in the head
+    fn create_link(&self, props: LinkProps) {
+        self.document.create_link(props);
+    }
+
+    fn create_head_component(&self) -> bool {
+        !head_element_written_on_server()
+    }
+}