CMake: Use of CMAKE_Swift_MODULE_DIRECTORY breaks Xcode and Ninja Multi-Config generators

[dabrahams]

Please see the warning here. As it stands if you want to generate a working Xcode project that uses ArgumentParser from CMake, you're out of luck.

These changes modernize the use of CMake by eliminating potentially problematic consolidation of output directories across dependent projects, and work around Swift bug swiftlang/swift#72841.

ArgumentParser version: the main branch