Transition to pybind11 and shared python
This MR moves the python scripting out of pcbnew and into its own KIFACE.
Allows sharing the scripting instance between pcbnew and eeschema and main KiCad window.
Removes a number of build flags:
KICAD_SCRIPTING = on
KICAD_SCRIPTING_PYTHON3 = on
KICAD_SCRIPTING_WXPYTHON_PHOENIX = on
KICAD_SCIRPTING_ACTION_PLUGINS = on
All of these options are now default and required. Python3 is required to build.
Retained build option is:
KICAD_SCRIPTING_WXPYTHON = on
This allows users to disable WXPYTHON for building if their platform does not support it. This is currently the case for msys2/mingw.