RBTools has historically been a setuptools-based project, relying

heavily on the dynamic ability of setup.py. Over the years, the Python

ecosystem has moved to pyproject.toml files, with pluggable build

backends. This has reached a point of maturity, and pip will soon

remove support for installing either production or editable installs

from a legacy source tree.
We now use pyproject.toml to define all of the metadata of the

package. Since RBTools's packaging needs are simple, we can get away

with using the setuptools.build_meta backend directly.

Tested isolated builds in the following setups:

python -m build . (builds sdist, then a wheel from the sdist)
python -m build . -s (builds sdist)
python -m build . -w (builds wheel)

Tested isolated editable installs using pip install -e . and

non-isolated editable installs using pip install -e --no-build-isolation

and with make develop.
Performed full tree diffs of generated wheels from ./setup.py bdist_wheel

(prior to this change) and both wheel-producing python -m build methods.

Verified that all content was identical, with the exception of differences

in source map paths and some modern metadata for the package.
Manually inspected the distribution contents to make sure we had everything

we want in the package and nothing we don't want.