chore: remove critical circular dependencies (#8114)

* chore: remove critical circular dependencies

* chore: fix tslint errors

* chore: remove platform specific types from interfaces

* chore: update unit tests polyfills

* fix: incorrect null check

* chore: update api.md file

* test: improve test case

* chore: apply comments

* test: avoid page style leaks in tests

nativescript-core/application/application.d.ts

@@ -211,15 +211,6 @@ export function run(entry?: NavigationEntry | string);
  */
 export function _resetRootView(entry?: NavigationEntry | string);
 
-/**
- * @private
- */
-export function _shouldCreateRootFrame(): boolean;
-/**
- * @private
- */
-export function _start(entry?: NavigationEntry | string);
-
 /**
  * A basic method signature to hook an event listener (shortcut alias to the addEventListener method).
  * @param eventNames - String corresponding to events (e.g. "onLaunch"). Optionally could be used more events separated by `,` (e.g. "onLaunch", "onSuspend").
@@ -610,7 +601,7 @@ export class AndroidApplication extends Observable {
 /**
  * The abstraction of an iOS-specific application object.
  */
-export interface iOSApplication {
+export class iOSApplication {
     /* tslint:enable */
     /**
      * The root view controller for the application.