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/file_upload.rs

@@ -43,7 +43,7 @@ fn app() -> Element {
     };
 
     rsx! {
-        head::Link { rel: "stylesheet", href: STYLE }
+        document::Link { rel: "stylesheet", href: STYLE }
 
         h1 { "File Upload Example" }
         p { "Drop a .txt, .rs, or .js file here to read it" }