.NET Core Theme Styles for WPF Controls

Create a standard set of Theme Styles.

At present, an older copy of these styles can be found in Visual Studio, which were created in ~.NET 4.5 timeframeframe.

```
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\aero.normalcolor.xaml
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\aero2.normalcolor.xaml
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\aerolite.normalcolor.xaml
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\classic.xaml
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\luna.homestead.xaml
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\luna.metallic.xaml
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\luna.normalcolor.xaml
C:\Program Files (x86)\Microsoft Visual Studio\2019\Preview\DesignTools\SystemThemes\Wpf\royale.normalcolor.xaml
```

The theme specific XAML files (#865) do not contain enough information to be used as-is (#1146).

- The Theme Styles that we ship with VS should be updated to correspond with recent .NET Core sources.
- We should have a way of generating these theme styles automatically from our sources.

Further, we should work with the VS templating team to ensure that these update Theme Styles are available as an item-template and consumable by the VS IDE at design-time.