Add query segment example and documentation (#1417)

* fix a few new clippy lints

* Add query segment example

* Add trait documentation

* Change core package to root package

The core package contains the virtual dom implementation ([here](https://github.com/DioxusLabs/dioxus/tree/master/packages/core)). Root package might be a more clear way to refer to the main directory

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Co-authored-by: Evan Almloff <evanalmloff@gmail.com>

packages/web/src/dom.rs

@@ -392,6 +392,7 @@ fn read_input_to_data(target: Element) -> Rc<FormData> {
         .dyn_ref()
         .and_then(|input: &web_sys::HtmlInputElement| {
             input.files().and_then(|files| {
+                #[allow(clippy::arc_with_non_send_sync)]
                 crate::file_engine::WebFileEngine::new(files)
                     .map(|f| std::sync::Arc::new(f) as std::sync::Arc<dyn dioxus_html::FileEngine>)
             })