web: fix dual-select with dynamic selection (#11133)

* web: fix dual-select with dynamic selection

For dynamic selection, the property name is `.selector` to message that it's a function the
API layer uses to select the elements.

A few bits of lint picked.

* web: added comment to clarify what the fallback selector does

web/src/elements/ak-dual-select/ak-dual-select-dynamic-selected-provider.ts

@@ -50,3 +50,9 @@ export class AkDualSelectDynamic extends AkDualSelectProvider {
         ></ak-dual-select>`;
     }
 }
+
+declare global {
+    interface HTMLElementTagNameMap {
+        "ak-dual-select-dynamic-selected": AkDualSelectDynamic;
+    }
+}