Build with PyPy3

Other “python_targets” USE_EXPAND flag values

Use FlagDescription
python_targets_pypy3Build with PyPy3
python_targets_python3_10Build with Python 3.10
python_targets_python3_11Build with Python 3.11
python_targets_python3_12Build with Python 3.12

All packages providing a “python_targets_pypy3” USE flag (757)