Understand CPS support

[mschofie]

There should be an exploration into .cps support. CMake 4.0 will find .cps files and manifest them in CMake. Things to think about:

1. It could be that the PROBE_PATHS simply needs to accommodate .cps files...?
2. Perhaps take an existing, simple, overlay and make a .cps representation of it
3. Once responsibilities of the winmd projection have settled (see .winmd NuGet packages should have a more abstract representation #6), can a .winmd-based-NuGet package represent itself purely as a .cps file?