Move the document trait into a separate crate (#3035)

* add a default head method through eval
* remove the old document trait
* implement document for each platform
* pull out document into a dedicated crate to cut down on shared dependencies
---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

examples/flat_router.rs

@@ -14,7 +14,7 @@ const STYLE: &str = asset!("./examples/assets/flat_router.css");
 fn main() {
     dioxus::launch(|| {
         rsx! {
-            head::Link { rel: "stylesheet", href: STYLE }
+            document::Link { rel: "stylesheet", href: STYLE }
             Router::<Route> {}
         }
     })