Uno is not strict enough about non-existent resources

[MartinZikmund]

Current behavior

Consider the following in a blank app's MainPage.xaml:

<StackPanel
    HorizontalAlignment="Center"
    VerticalAlignment="Center"
    Background="{ThemeResource NopeNotExisting}">
    <TextBlock
        HorizontalAlignment="Center"
        AutomationProperties.AutomationId="HelloTextBlock"
        Foreground="{StaticResource DoesNotExistAtAll}"
        Text="Hello Uno Platform" />
</StackPanel>

When run, the app starts up fine on Uno targets

Expected behavior

The app crashes on WinUI, we should match this behavior, as this potentially hides issues.

How to reproduce it (as minimally and precisely as possible)

No response

Workaround

No response

Works on UWP/WinUI

Yes

Environment

No response

NuGet package version(s)

No response

Affected platforms

No response

IDE

No response

IDE version

No response

Relevant plugins

No response

Anything else we need to know?

No response

[MartinZikmund]

This issue may be even more problematic for Converters:

https://github.com/unoplatform/Uno.Gallery/pull/1116/files#diff-035d07c81e29b43ad51842f2e153c5be6d9d79fe0a6ac7c83979d28b8dc58104L1424-L1427