TabViewItem can no longer be a child of TabView

[michael-hawker]

Describe the bug
If you try and add a TabViewItem as the content of a TabView as in this docs example you get an error:

TabView does not support TabViewItem as content.

(I feel like this may be a regression as the docs were probably valid at one point.)

In WinUI 2.3, you need to instead encase the TabViewItems in a special <muxc:TabView.TabItems> property.

Steps to reproduce the bug

Steps to reproduce the behavior:

1. Open XAML Studio
2. Paste in the example from the docs:

    <muxc:TabView HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
        <muxc:TabViewItem Header="Home" />
        <muxc:TabViewItem Header="Document 1" />
        <muxc:TabViewItem Header="Document 2" />
        <muxc:TabViewItem Header="Document 3" />

        <muxc:TabView.TabStripHeader>
            <Grid x:Name="ShellTitlebarInset" Background="Transparent" />
        </muxc:TabView.TabStripHeader>
        <muxc:TabView.TabStripFooter>
            <Grid x:Name="CustomDragRegion" Background="Transparent" />
        </muxc:TabView.TabStripFooter>
    </muxc:TabView>

Note: the Icon property from the example was also removed, as modified the above.

Expected behavior
Should display tabs without needing to wrap in TabItems property:

        <muxc:TabView.TabItems>
            <muxc:TabViewItem Header="Home" />
            <muxc:TabViewItem Header="Document 1" />
            <muxc:TabViewItem  Header="Document 2" />
            <muxc:TabViewItem  Header="Document 3" />
        </muxc:TabView.TabItems>

Version Info
WinUI 2.3.191129002

Additional context
Reference #1332

[ranjeshj]

@stmoy It looks like this is not working because TabItems is not the content property for TabView. We can either update the sample or make it as the content property.

[michael-hawker]

It'd be nice to see it as the content property, as that's a pretty standard practice. It's always nice to be able to type less. 🙂

[stmoy]

In the same way that one can add ListViewItems to ListView, I feel that we should be able to do the same with TabView.