Example uses obsolete API

The FormattedText constructor used in the example is marked as obsolete.

Please update with other constructor.

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#### Document Details

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* ID: eddeed1d-cae8-c0c0-43f6-03516cc0ff56
* Version Independent ID: 829cde58-83a3-42c8-cdd9-bb46252d8fa0
* Content: [How to: Draw Text to a Control's Background - WPF .NET Framework](https://docs.microsoft.com/en-us/dotnet/desktop/wpf/advanced/how-to-draw-text-to-a-control-background?view=netframeworkdesktop-4.8)
* Content Source: [dotnet-desktop-guide/framework/wpf/advanced/how-to-draw-text-to-a-control-background.md](https://github.com/dotnet/docs-desktop/blob/master/dotnet-desktop-guide/framework/wpf/advanced/how-to-draw-text-to-a-control-background.md)
* Product: **dotnet-framework**
* Technology: **dotnet-wpf**
* GitHub Login: @adegeo
* Microsoft Alias: **adegeo**