WinUI 3, C++/WinRT, and Xaml with CMake

Requirements

• CMake 3.23 (April 2022) with the MSBuild generator is required
• Windows App SDK 1.1 (June 2022); this uses self-contained mode to solve several problems, which is new in 1.1

Notes

• Xaml-related header files must be listed as targert sources
• The Directory.Build.targets file is currently required; it slightly modifies the CMake generator
• I've avoided use namespace to be explicit; I'm not aiming for this to be 'best practice', just to be unambiguous and minimal
• pch.h and its' contents are required by the generated code
• pch.h is not currently a pre-compiled header