Consider using CPack when building Xcframeworks and Android lib dirs

[kraenhansen]

If we used CPack as a part of building Node-API module prebuilds, I suspect we'll be able to:

• make less assumptions on the structure of the artifacts produced by projects and
• defer til CMake to extract public header files for the projects.

There's no XCFramework generator for CPack, but I suspect the External generator is what we need: https://cmake.org/cmake/help/latest/cpack_gen/external.html