[TIMOB-24843] iOS: When using "Ti.UI.NavigationWindow.popToRootWindow", fire "close" event for all sub-windows, cleanup proxy stack more properly

We introduced the popToRootWindow in 6.0.0 (TIMOB-23567) to allow the user to close all windows of a Ti.UI.iOS.NavigationWindow at once. While that works pretty well, the proxies behind the closed windows might still be active, causing a possible memory leak. Another thing is that, currently, only the close event of the latest window is triggered, which is aligned to the native behavior of the viewDidDisappear delegate method. So firing all close events would be an improvement for more specific window-control. So the changes described in this ticket are: 1. Fire the close event on all pushed windows of the nav-window 2. Cleanup all window-proxies after calling the internal API to improve the memory-management when using the method (Created per discussion in TIMOB-23567)