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/file_upload.rs

@@ -0,0 +1,99 @@
+//! This example shows how to use the `file` methods on FormEvent and DragEvent to handle file uploads and drops.
+//!
+//! Dioxus intercepts these events and provides a Rusty interface to the file data. Since we want this interface to
+//! be crossplatform,
+
+use dioxus::html::HasFileData;
+use dioxus::prelude::*;
+use dioxus_html::FileData;
+
+const STYLE: Asset = asset!("/examples/assets/file_upload.css");
+
+fn main() {
+    dioxus::launch(app);
+}
+
+struct UploadedFile {
+    name: String,
+    contents: String,
+}
+
+fn app() -> Element {
+    let mut enable_directory_upload = use_signal(|| false);
+    let mut files_uploaded = use_signal(|| Vec::new() as Vec<UploadedFile>);
+    let mut hovered = use_signal(|| false);
+
+    let upload_files = move |files: Vec<FileData>| async move {
+        for file in files {
+            let filename = file.name();
+            if let Ok(contents) = file.read_string().await {
+                files_uploaded.write().push(UploadedFile {
+                    name: filename,
+                    contents,
+                });
+            } else {
+                files_uploaded.write().push(UploadedFile {
+                    name: filename,
+                    contents: "Failed to read file".into(),
+                });
+            }
+        }
+    };
+
+    rsx! {
+        Stylesheet { href: STYLE }
+
+        h1 { "File Upload Example" }
+        p { "Drop a .txt, .rs, or .js file here to read it" }
+        button { onclick: move |_| files_uploaded.write().clear(), "Clear files" }
+
+        div {
+            label { r#for: "directory-upload", "Enable directory upload" }
+            input {
+                r#type: "checkbox",
+                id: "directory-upload",
+                checked: enable_directory_upload,
+                oninput: move |evt| enable_directory_upload.set(evt.checked()),
+            }
+        }
+
+        div {
+            label { r#for: "textreader", "Upload text/rust files and read them" }
+            input {
+                r#type: "file",
+                accept: ".txt,.rs,.js",
+                multiple: true,
+                name: "textreader",
+                directory: enable_directory_upload,
+                onchange: move |evt| async move {
+                    upload_files(evt.files()).await
+                },
+            }
+        }
+
+        div {
+            id: "drop-zone",
+            background_color: if hovered() { "lightblue" } else { "lightgray" },
+            ondragover: move |evt| {
+                evt.prevent_default();
+                hovered.set(true)
+            },
+            ondragleave: move |_| hovered.set(false),
+            ondrop: move |evt| async move {
+                evt.prevent_default();
+                hovered.set(false);
+                upload_files(evt.files()).await;
+            },
+            "Drop files here"
+        }
+
+        ul {
+            for file in files_uploaded.read().iter().rev() {
+                li {
+                    span { "{file.name}" }
+                    pre  { "{file.contents}"  }
+                }
+            }
+        }
+    }
+}