Allow multiple prevent default for Web, Desktop and LiveView (#987)

* Allow multiple prevent default in dioxus_web

* Use SplitWhitespace for prevent default requests

* Add multiple prevent default option to liveview and desktop

* Update docs about prevent_default attribute

* cargo clippy

* update prevent default guide example

---------

Co-authored-by: Evan Almloff <ealmlof1@stumail.jccc.edu>

docs/guide/examples/event_prevent_default.rs

@@ -10,8 +10,7 @@ fn App(cx: Scope) -> Element {
     // ANCHOR: prevent_default
 cx.render(rsx! {
     input {
-        prevent_default: "oninput",
-        prevent_default: "onclick",
+        prevent_default: "oninput onclick",
     }
 })
     // ANCHOR_END: prevent_default