RelativePanel - edge cases...

[danwalmsley]

Describe the bug
A clear and concise description of what the bug is.
I tried the msft example from:

https://docs.microsoft.com/en-us/windows/uwp/design/layout/layout-panels

<RelativePanel BorderBrush="Gray" BorderThickness="1">
    <Rectangle x:Name="RedRect" Fill="Red" Height="44" Width="44"/>
    <Rectangle x:Name="BlueRect" Fill="Blue"
               Height="44" Width="88"
               RelativePanel.RightOf="RedRect" />

    <Rectangle x:Name="GreenRect" Fill="Green" 
               Height="44"
               RelativePanel.Below="RedRect" 
               RelativePanel.AlignLeftWith="RedRect" 
               RelativePanel.AlignRightWith="BlueRect"/>
    <Rectangle Fill="Orange"
               RelativePanel.Below="GreenRect" 
               RelativePanel.AlignLeftWith="BlueRect" 
               RelativePanel.AlignRightWithPanel="True"
               RelativePanel.AlignBottomWithPanel="True"/>
</RelativePanel>

It should look like:

But this implementation gives:

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior
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Screenshots
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Environment (please complete the following information):

• .net: [e.g. 4.6.2]
• IDE [e.g. vs2017]
• Version [e.g. 1.0.0]

Additional context
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