Errors setting some properties on root of XAML file

[carldebilly]

GitHub Issue (If applicable): #718

Bugfix

Description of the bug

Setting a collection-based property on the root of a XAML file like this
were leading to c# compilation errors:

<Grid
	x:Class="XamlGenerationTests.Shared.GridAsRoot"
	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"> 
	<Grid.ColumnDefinitions>
		<ColumnDefinition />
	</Grid.ColumnDefinitions>
</Grid>

PR Checklist

Please check if your PR fulfills the following requirements:

• Tested code with current supported SDKs
• Docs have been added/updated which fit documentation template. (for bug fixes / features)
• Unit Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• Contains NO breaking changes
• Updated the Release Notes
• Associated with an issue (GitHub or internal)

[davidjohnoliver]

There are a couple of related issues in the backlog. @carldebilly would you mind testing to see if they're fixed so we could close them?

#856
#211