[Feature] Easier back button press handling - source generator

[BurkusCat]

Is your feature request related to a problem? Please describe. Having to override ContentPage etc. with BurkusContentPage is a hassle.

Describe the solution you'd like Source generators should automatically add the below code to any ContentPage etc:

    protected override bool OnBackButtonPressed()
    {
        return BackButtonNavigator.HandleBackButtonPressed();
    }

Describe alternatives you've considered N/A

Proposed APIs A builder method to disable the automatic behaviour? Should there still be a way to manually set this on each page?

Additional context How would this work with pages defined in code rather than in.xaml.cs?