Bootstrap re-order: Build setuptools --with bootstrap with python3-rpm-generators
The generators only need packaging and packaging only needs flit.core.
We can now build:
0. python-rpm-macros bumped to 3.N
1. python3.N --with bootstrap ...
2. python-flit --with bootstrap
3. python-packaging --with bootstrap
4. python-setuptools --with bootstrap (already using the generators at this point)
5. ...