Shorthand for RowDefinitions and ColumnDefinitions

[Arlodotexe]

Creating Grid RowDefinitions and ColumnDefinitions in XAML can be quite verbose:

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="300"/>
        <RowDefinition Height="*"/>
        <RowDefinition Height="2*"/>
    </Grid.RowDefinitions>

    <Button />
    <Button Grid.Row="1"/>
    <Button Grid.Row="2"/>
</Grid>

Rather than type that out every time, we could create a shorthand that reduces this code to something like:

<Grid wct:RowDefinitions="300,*,2">
    <Button />
    <Button Grid.Row="1"/>
    <Button Grid.Row="2"/>
</Grid>

[michael-hawker]

This is already a feature in WinUI 3: microsoft/microsoft-ui-xaml#673 - Though not sure where the VS bug is for the tooling being broken, maybe a new one needs to be filed?

Don't feel like we should polyfill just for UWP for this one, as convenient as it can be.