Adding C++ Custom conditional predicate sample for WinUI3

[Hemantxk]

Description

This PR adds a WinUI sample of using Custom Xaml predicate by implementing IXamlPredicate. IXamlPredicate interface is added in WinAppSDK 2.0 experimental 4 release, this PR show case it's usage.

Target Release

Please specify which release this PR should align with. e.g., 1.0, 1.1, 1.1 Preview 1.

Checklist

Note that /azp run currently isn't working for this repo.

• Samples build and run using the Visual Studio versions listed in the Windows development docs.
• Samples build and run on all supported platforms (x64, x86, ARM64) and configurations (Debug, Release).
• Samples set the minimum supported OS version to Windows 10 version 1809.
• Samples build clean with no warnings or errors.
• [For new samples]: Samples have completed the sample guidelines checklist and follow standardization/naming guidelines.
• Microsoft employees only: you can validate your changes by following the instructions here: https://www.osgwiki.com/wiki/WindowsAppSDK-Samples

[Hemantxk]

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