feat(core): initRootView event (#10442)

launchEvent is not triggered at the same moment on iOS and Android. 
iOS is firing after setting the rootView while Android is firing before.
Consequently if you need an event for when the rootView is set (to read/write root css variables) you need this event.

[skip ci]

packages/core/application/application-interfaces.ts

@@ -117,6 +117,13 @@ export interface CssChangedEventData extends ApplicationEventData {
 	cssText?: string;
 }
 
+/**
+ * Event data containing information about application css change.
+ */
+export interface InitRootViewEventData extends ApplicationEventData {
+	rootView: View;
+}
+
 /**
  * Data for the Android activity events.
  */