Improving samples for build2022

[marb2000]

Description

These samples have been modified for a better understanding of the XAML/WinUI concepts.

• Improving TitleBar sample,
• Improving and adding a new sample for Creating Multiple WIndow,
• Improving ItemsRepeater sample with the DataModel code and adding Layout and DataTemplete as Resource of the ScrollViewer
• Improving AnimationsInterop sample - There was an error when copy&paste the code in WinUI3, there is no App.Current in desktop, and the Compositor comes from the Window object.
• Improving ContentDialog sample, the sample code for getting the XamlRoot was very fragile
• Fixing bug in Mica CS code sample. There was a ; after a class definition.

Motivation and Context

I have modified several samples to help users understand the WinUI/XAML concepts better and avoid users going back and forward from docs to the WinUI Gallery.

How Has This Been Tested?

Smoke tests in the WinUI3 project.

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)