Better identification of broken Distribution objects

Currently, I'm getting an error on Python 3.8 and 3.9 in https://github.com/pypa/build/pull/820:

docker run --rm -it python:3.9 bash
pip install tox
git clone https://github.com/pypa/build
cd build
tox -e py39 -- -k test_metadata_path_no_prepare -v

...
File "/build/.tox/py39/lib/python3.9/site-packages/importlib_metadata/compat/py39.py", line 23, in normalized_name
    return Prepared.normalize(getattr(dist, "name", None) or dist.metadata['Name'])
  File "/build/.tox/py39/lib/python3.9/site-packages/importlib_metadata/__init__.py", line 889, in normalize
    return re.sub(r"[-_.]+", "-", name).lower().replace('-', '_')
  File "/usr/local/lib/python3.9/re.py", line 210, in sub
    return _compile(pattern, flags).sub(repl, string, count)
TypeError: expected string or bytes-like object

The problem is dist.__dict__={'_path': PosixPath('/build/tests/packages/test-no-prepare/test_no_prepare.egg-info')}. I think this is tripping up on tests/packages/test-no-prepare/test_no_prepare.egg-info/ and the local backend. But I don't know what updated to cause this to start happening.

Regardless of the solution, though, I think the handling here for a missing name should be better, there wasn't any useful info in the error message to tell me about the dist that was failing. I had to add print(f"{dist.__dict__=}") to see it. Or maybe the normalize name could return None, and let the failure happen elsewhere.

Start by reproducing the failure with the Python 3.9 Docker and tox commands in the issue, then read normalized_name in importlib_metadata/compat/py39.py and normalize in importlib_metadata/init.py. Trace how the Distribution with only _path reaches name normalization; done means a missing or invalid name produces useful identification of the failing distribution and the relevant tests pass.