python-utils-r1.eclass: Do not prefer Jython & PyPy over CPython

python-utils-r1.eclass: Do not prefer Jython & PyPy over CPython

Fix _PYTHON_ALL_IMPLS to list Jython & PyPy before CPython versions,
therefore causing them not to be implicitly preferred over CPython.

The implementation reordering done in b284e54 ("reorder implementations
in semi-ascending order") has caused PyPy & Jython to be listed after
CPython. While seemingly it was more intuitive to list third-party
implementations after the reference one, it also implicitly caused them
to be preferred by python-exec.