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

examples/calculator_mutable.rs

@@ -29,7 +29,7 @@ fn app() -> Element {
     let mut state = use_signal(Calculator::new);
 
     rsx! {
-        head::Link { rel: "stylesheet", href: asset!("./examples/assets/calculator.css") }
+        document::Link { rel: "stylesheet", href: asset!("./examples/assets/calculator.css") }
         div { id: "wrapper",
             div { class: "app",
                 div {