Revive CMake support
It seems, at least on the Android front, quite some things have improved in terms of Multi-ABI support, see this blog post: https://www.qt.io/blog/qt-5.14-android-multi-abi-and-cmake
We could consider reviving the cmake build for the app, as this still somehow seems to be the better way forward. Ideally, however, this is also done in conjunction with moving the iOS build to cmake.
Currently, the app is supported on a list of target operating systems and architectures. Ideally, we could use
cmake for all of them (and then do the final switch). The list is: