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/resize.rs

@@ -15,7 +15,7 @@ fn app() -> Element {
     let mut dimensions = use_signal(Size2D::zero);
 
     rsx!(
-        head::Link { rel: "stylesheet", href: asset!("./examples/assets/read_size.css") }
+        document::Link { rel: "stylesheet", href: asset!("./examples/assets/read_size.css") }
         div {
             width: "50%",
             height: "50%",