fix: View not added to this instance.

[CatchABus]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• All existing tests are passing: https://github.com/NativeScript/nativescript-angular/blob/master/DevelopmentWorkflow.md#running-the-tests
• Tests for the changes are included.

What is the current behavior?

When pressing 'back' to exit application, an Activity-related exception is thrown.
This behaviour is also met when creating a basic angular application using 'tns create'.
So far, it's confirmed in android platform.

What is the new behavior?

Exception issues will be fixed using a small hack. It would be great if AppHostView parent behaviour was improved in the future.

Fixes: NativeScript/NativeScript#8667

[CatchABus]

This fix helps page-router-outlet remove the temporary presence of a component from AppHostView.
This occurs when page-router-outlet is the direct child of root view.
My '_addView' addition cooperates with the following line to ensure that component is passed from one parent to another with success: https://github.com/NativeScript/nativescript-angular/blob/master/nativescript-angular/router/page-router-outlet.ts#L374

I tested it and had no issues, but still I'm not an Angular expert so I ask that my contribution is tested thoroughly.

[CatchABus]

I'm closing this since NS team has done some amazing work on Angular, including a fix for this issue.