The calculator I always wanted

[vanLudwig]

The buttons getting clipped at the bottom of the screen were caused by improper handling of the camera cutout. I have a fix in hand for this issue. As a bonus, the app now consumes the whole screen rather than leaving the space above the camera black.

I'm pretty sure this is the problem with the back button: https://github.com/xamarin/Xamarin.Forms/issues/7311. Looks like they have it fixed in Xamarin Forms, but I don't think they've released a patch yet.