Python Cleanup + Yosys Updates

[donn]

• Created buildPythonEnvForInterpreter, which can be used for applications embedding Python interpreters (e.g. KLayout) to provide a passthru withPythonPackages method
• Updated KLayout to 0.29.4
  • withPythonPackages method added to add packages to built-in Python interpreter
  • klayout-pymod moved as a passthru named klayout.pymod
• Updated Yosys to 0.44
  • Yosys and YosysHQ plugins now use versions instead of revs
  • Now built with Pyosys enabled, module accessible via yosys.pymod
  • yosys-ghdl plugin now also available on x86_64-darwin
  • yosys-abc now moved inside same file as yosys, uses abc tarball from yosys release
  • Patched in -y flag for libyosys Python scripts YosysHQ/yosys#4553
• Cleaned up metadata
• Cleaned up rec{ blocks