WPFHostingWin32Control sample and walkthrough missing RegisterTouchWindow()

**Issue description**

The [WPFHostingWin32Control sample](https://github.com/Microsoft/WPF-Samples/tree/master/Migration%20and%20Interoperability/WPFHostingWin32Control) and [walkthrough](https://docs.microsoft.com/en-us/dotnet/framework/wpf/advanced/walkthrough-hosting-a-win32-control-in-wpf) are missing a call to [RegisterTouchWindow()](https://docs.microsoft.com/en-us/windows/win32/api/winuser/nf-winuser-registertouchwindow). Without this the win32 child window will receive mouse and keyboard events, but not touch (WM_TOUCH) or gesture events.

**Target framework**

Check the .NET target framework(s) being used, and include the version number(s).

- [ ] .NET Core
- [ ] .NET Standard
- [x] .NET Framework

If using the .NET Core SDK, include `dotnet --info` output. If using .NET Framework without the .NET Core SDK, include info from Visual Studio's **Help** > **About Microsoft Visual Studio** dialog.

About VS info

```console
Microsoft Visual Studio Professional 2017
Version 15.9.16
VisualStudio.15.Release/15.9.16+28307.858
Microsoft .NET Framework
Version 4.7.03062

Installed Version: Professional

Visual C++ 2017 00370-20004-56286-AA303
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Application Insights Tools for Visual Studio Package 8.14.20131.1
Application Insights Tools for Visual Studio

ASP.NET and Web Tools 2017 15.9.04012.0
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C# Tools 2.10.0-beta2-63501-03+b9fb1610c87cccc8ceb74a770dba261a58e39c4a
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Common Azure Tools 1.10
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IntelliCode Extension 1.0
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JavaScript Language Service 2.0
JavaScript Language Service

JavaScript Project System 2.0
JavaScript Project System

JavaScript UWP Project System 2.0
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Markdown Editor 1.12.253
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Microsoft JVM Debugger 1.0
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NuGet Package Manager 4.6.0
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Installs the individual extensions of Productivity Power Tools 2017/2019

ProjectServicesPackage Extension 1.0
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TypeScript Tools 15.9.30718.2001
TypeScript Tools for Microsoft Visual Studio

Visual Basic Tools 2.10.0-beta2-63501-03+b9fb1610c87cccc8ceb74a770dba261a58e39c4a
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Visual C++ for Linux Development 1.0.9.28218
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Visual Studio Tools for CMake 1.0
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Visual Studio Tools for Universal Windows Apps 15.0.28307.858
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```