Provide an add_application function which would call add_executable or add_library depending on platform

Qt application developers that use CMake and want to write an application targeting both iOS and Android end up having to write:

if(ANDROID)
  add_library(MyApp)
elseif(APPLE)
  add_executable(MyApp)
endif()

This is because on Android, the native C++ part of the application ends up being compiled into a shared library, which is then dynamically loaded (dlopened) by the appropriate .jar / Java runtime.

Instead of forcing users to write these if() conditions, it would be nice if CMake provided a function called add_application which hides the conditional logic inside the function body.

Related upstream issue: https://gitlab.kitware.com/cmake/cmake/-/issues/20864