[Android] Navigation dont wait initial pages to be loaded on AppCompat

[kvpt]

Description

If you want to navigate to another page in the OnStart method, auto login for exemple, and if you navigate to fast, the page will load before the MainPage and will be wipped by the MainPage loaded after.
The state of the navigation stack will be inconsistant and it will cause differents issues or crash like IndexOutOfRange.

The FormsApplicationActivity works as excepted.

Steps to Reproduce

1. Create an Xamarin Forms Android from the template
2. In App class set a NavigationPage as MainPage
3. In the OnStart method push a new page
   await Current.MainPage.Navigation.PushAsync(new Page { Title = "New" });
4. Launch application

Expected Behavior

The page displayed is the page loaded in OnStart
And if you go back it's your MainPage

Actual Behavior

The page displayed is the original page and the page loaded in OnStart is "phantom", if you press go back it throw an IndexOutOfRangeException.

[hartez]

@kvpt If I open your repro and make these changes to NavigationPageRenderer.OnAttachedToWindow(), I get an ArgumentOutOfRangeException.

[kvpt]

@hartez You're right, I have made a more complex reproduction to test this case and forgot to test if the first reproduction case was still fixed, and indeed it's not the case.
I will try to fix this asap later in the week.

[kvpt]

@hartez I fixed it, you can review it again.

[samhouts]

Duplicate of #3528