This changeset allows for cross-compilation of Python packages. Packages
built with buildPythonPackage are not allowed to refer to the build
machine. Executables that have shebangs will refer to the host.
This continues #23374, which always kept around both attributes, by
always including both propagated files: `propgated-native-build-inputs`
and `propagated-build-inputs`. `nativePkgs` and `crossPkgs` are still
defined as before, however, so this change should only barely
observable.
This is an incremental step to fully keeping the dependencies separate
in all cases.
Thus far all executables in a derivation were wrapped. This commit
only wraps executables in $out/bin. If other scripts need to be wrapped
as well, then one can use wrapPythonProgramsIn.
