Proposal: TabViewItem should respect CornerRadius API

Summary

To set the corner radius of a TabViewItem, developers today have to override the OverlayCornerRadius resource. They should also be able to use the TabViewItem.CornerRadius API for that.

Example

<muxc:TabView>
    <muxc:TabView.TabItems>
        <muxc:TabViewItem Header="Tab 1" CornerRadius="0">
            Some tab content
        </muxc:TabViewItem>
    </muxc:TabView.TabItems>
</muxc:TabView>

Additional Context

This proposal is related to a few other TabViewItem issues like #3047 and #2653. @stmoy FYI