Readable and Writable helpers for String, HashMap and HashSet (#4834)

* Add more read/write methods for string signals

* add helpers for HashMap and HashSet as well

* fix typo

* fix conflicting string and str extensions

* fix counters example

examples/08-apis/control_focus.rs

@@ -56,7 +56,7 @@ fn app() -> Element {
                 input {
                     r#type: "number",
                     value: "{i}",
-                    onmounted: move |cx| elements.write().push(cx.data()),
+                    onmounted: move |cx| elements.push(cx.data()),
                     oninput: move |_| running.set(false),
                 }
             }