Do not default to Apple Watch as default for Simulator

As we do not support this platform in Qt anyway and it's usually not what people target, I hope we can default to something more sensible like an iPhone target by default.
Especially with CMake projects it should be rather easy to switch to a reasonable default based on CMAKE_SYSTEM_NAME, which can be either ios, watchos or appletvos.

It might also be nice to be able to just pick a custom default simulator to use if no other is specified somewhere in settings but I'm not sure if that's possible or already exists.