Meson subprojects just have too many problems and limitations and I can foresee
the maintenance headache and the future incoming false-positive bug reports if
we start using meson subprojects.
Comparing to the simplicity of git submodule which also has much better
notifications to help people understand when the submodule is not in sync and
how to remedy to it.
See commit gimp-data@c364adb explaining the main reasons in detail.
Eventually all executables will have the manifest and version resources
linked. In this initial step, the current resources are moved from the
app/ directory to a global build/windows directory.
