Currently, for all of the desktop builds, we trigger the native build (Xcode, make, etc.) and that eventually calls into the backend script that copies engine artifacts like the library and the C++ client wrappers.

I'm in the process of converting Linux (and maybe Windows) to CMake, and with CMake the best option is to have the build files live next to the things they are building; in the case of then engine artifacts it would not only make the build structure cleaner and more modular, but it would mean that we could retain long-term control over those files. For instance, the client wrapper targets could be updated if the set of client wrapper files changed, without breaking existing consumers.

However, the CMake step is the very first step in the build, so we can't call it without already having all the CMakeLists.txt files in place. In order for them to live with the artifacts, we'd need to be able to trigger the artifact copying earlier, from, e.g., build_linux.dart, just before doing CMake generation.

/cc @jonahwilliams