BoxView in Grid Auto Row doesn't get sized properly based on RowDefinition Height value

### Description

The NestedGrid demo from the Xamarin Forms samples repo doesn't render similarly when ported to MAUI:

The XAML is as follows:
```

```

In investigating this, setting row definitions to different values produces unexpected results:

1. These work properly:
- `


`
- `


`
- `


`
2. This causes BoxView to take up the whole Grid:
- `


`
3. This causes BoxView to not take up any space (the original issue)
`


`

### Steps to Reproduce

1. Port the following to MAUI: https://github.com/xamarin/xamarin-forms-samples/tree/main/UserInterface/Layout/GridDemos
2. Run the app without changing the XAML

### Version with bug

Preview 10 (current)

### Last version that worked well

Unknown/Other

### Affected platforms

iOS, Android

### Affected platform versions

iOS 15, Android Pixel 4 API 30

### Did you find any workaround?

Play around with RowDefinition Height values for the expected result.

### Relevant log output

_No response_

Start by porting the Xamarin.Forms GridDemos NestedGrid demo and running the supplied XAML on iOS and Android. Compare the BoxView size with the RowDefinition Height="Auto" and unspecified-height cases; done means the MAUI rendering matches the expected layout and the reported row-height variations behave consistently.

Written by the indexing model from the issue text.