Convert to modern Python packaging
    
    This way, we don't have outdated build dependencies.
    
    Before:
    
        python3-devel
        python3-mock
        python3-pytest
        python3-setuptools
        (python3dist(mccabe) < 0.7 with python3dist(mccabe) >= 0.6)
        python3dist(pycodestyle) < 2.8.0
        python3dist(pyflakes) < 2.4
    
    After:
    
        pyproject-rpm-macros
        python3-devel
        python3-pytest
        (python3dist(mccabe) < 0.7~~ with python3dist(mccabe) >= 0.6)
        python3dist(packaging)
        python3dist(pip) >= 19
        (python3dist(pycodestyle) < 2.9~~ with python3dist(pycodestyle) >= 2.8)
        (python3dist(pyflakes) < 2.5~~ with python3dist(pyflakes) >= 2.4)
        python3dist(setuptools) >= 40.8
        python3dist(wheel)