This PR should be treated as a proof of concept to adopt the new WASDK package format. Please feel free to build on or improve this when the time comes for the transition.

The major change is the single WASDK NuGet being separated into multiple packages. And the metadata, header and lib files got scattered into all those packages.

I've successfully build the python wheels except for Microsoft.Windows.ApplicationModel.Background.UniversalBGTask
This module creates the following error when building. I haven't looked into it too much.

py.Microsoft.Windows.ApplicationModel.Background.UniversalBGTask.cpp
py.Microsoft.Windows.ApplicationModel.Background.UniversalBGTask.cpp(71): error C2039: 'Run': is not a member of 'winrt::Microsoft::Windows::ApplicationModel::Background::UniversalBGTask::ITask'
D:\workspace\pywinrt\projection\winrt-WindowsAppSDK\src\winrt_windows_app_sdk\cppwinrt\winrt/impl/Microsoft.Windows.ApplicationModel.Background.UniversalBGTask.1.h(9): note: see declaration of 'winrt::Microsoft::Windows::ApplicationModel::Background::UniversalBGTask::ITask'

Another thing to take note is the number of NuGet packages is likely to increase in the future, as new features get into WASDK. So it may be better to come up with something more dynamic to handle all the paths.