Python: the pythonModule attribute

Python libraries or modules now have an attribute `pythonModule = interpreter;` to indicate
they provide Python modules for the specified `interpreter`.

The package set provides the following helper functions:

- hasPythonModule: Check whether a derivation provides a Python module.
- requiredPythonModules: Recurse into a list of Python modules, returning all Python modules that are required.
- makePythonPath: Create a PYTHONPATH from a list of Python modules.

Also included in this commit is:
- disabledIf: Helper function for disabling non-buildPythonPackage functions.

pkgs/development/interpreters/python/build-python-package.nix

@@ -5,7 +5,12 @@
 
 { lib
 , python
-, mkPythonDerivation
+, wrapPython
+, setuptools
+, unzip
+, ensureNewerSourcesHook
+, pythonModule
+, namePrefix
 , bootstrapped-pip
 , flit
 }:
@@ -15,6 +20,9 @@ let
   flit-specific = import ./build-python-package-flit.nix { inherit python flit; };
   wheel-specific = import ./build-python-package-wheel.nix { };
   common = import ./build-python-package-common.nix { inherit python bootstrapped-pip; };
+  mkPythonDerivation = import ./mk-python-derivation.nix {
+    inherit lib python wrapPython setuptools unzip ensureNewerSourcesHook pythonModule namePrefix;
+  };
 in
 
 {