The Python packaging world has long since recommended against eggs and

setup.py develop. However, until we move to a pyproject.toml with

a custom build system, this is our best option.
Review Board, Djblets, and other packages have implemented a custom

setup.py develop for ages, which wraps pip install -e . (the

generally preferred method) and then installs our development

dependencies.
This change adds the same logic to the RBTools packaging. This will

ensure that we don't ever introduce legacy eggs through RBTools for

development, and always prefer model wheels.
For now, setup.py develop is the preferred way of preparing RBTools

for development. In time, we will transition away from setup.py and

will prefer pip install -e ..

Successfully installed RBTools on Python 3.7-3.11, with all dependencies

as wheels, using setup.py develop.