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>

example-projects/file-explorer/src/main.rs

@@ -21,12 +21,12 @@ fn app() -> Element {
     let mut files = use_signal(Files::new);
 
     rsx! {
-        head::Link {
+        document::Link {
             rel: "stylesheet",
             href: asset!("./assets/fileexplorer.css")
         }
         div {
-            head::Link { href: "https://fonts.googleapis.com/icon?family=Material+Icons", rel: "stylesheet" }
+            document::Link { href: "https://fonts.googleapis.com/icon?family=Material+Icons", rel: "stylesheet" }
             header {
                 i { class: "material-icons icon-menu", "menu" }
                 h1 { "Files: " {files.read().current()} }