Add dependency WinUI 2.3 framework package

[licanhua]

Fix #3521
Fix #3695

It’s a breaking change, and you may be impacted:

• You are using an old version of WinUI like 2.1.
• You are using WinUI prelease
• Your product will not be shipped from Store. You may have to install WinUI dependency by yourself.

You have to manually add the Microsoft.UI.Xaml nuget to your project if you your app is created from old template

This is the integration with WinUI 2.3.191129002 framework package.

All our name space is 'react.uwp', so I changed 'RootNamespace' to make mdmerge.exe happy. and CppWinRTNamespaceMergeDepth is added to avoid compilation error because of RootNamespace change.

Microsoft Reviewers: Open in CodeFlow

[licanhua]

This is a redo of PR #3622 and make all project add reference of WinUI #Closed

[ddalp]