Create additional Grid helper for Names/SharedSizeGroup

[scottcg]

Consider adding an additional Grid helper to help when doing this:

<ColumnDefinitions>
  <ColumnDefinition x:Name="column1CloneForLayer0" SharedSizeGroup="column1" />
</ColumnDefinitions>

This also applies when referencing a size group and width:

<ColumnDefinitions>
  <ColumnDefinition Width="300" SharedSizeGroup="column1" />
</ColumnDefinitions>