Implement UI event dispatcher/listener (#4492)

* page change event
* expose event to plugin api
* Update UIPluginApi.md
* Add to example plugin
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Co-authored-by: WithoutPants <53250216+WithoutPants@users.noreply.github.com>

ui/v2.5/src/pluginApi.tsx

@@ -13,6 +13,7 @@ import * as FontAwesomeSolid from "@fortawesome/free-solid-svg-icons";
 import * as FontAwesomeRegular from "@fortawesome/free-regular-svg-icons";
 import { useSpriteInfo } from "./hooks/sprite";
 import { useToast } from "./hooks/Toast";
+import Event from "./hooks/event";
 import { before, instead, after, components, RegisterComponent } from "./patch";
 
 // due to code splitting, some components may not have been loaded when a plugin
@@ -106,6 +107,7 @@ export const PluginApi = {
     // and the result of the original function
     after,
   },
+  Event: Event,
 };
 
 export default PluginApi;