feat: Allow `-` in module name discovery

Feature

Can we allow - in module name discovery in https://mypy.readthedocs.io/en/stable/running_mypy.html#mapping-file-paths-to-modules
with a flag allow_all_module_names or something

such that we can do:

For example, say your directory tree consists solely of src/namespace-pkg/mod.py. If you run the following command, mypy will correctly associate mod.py with namespace-pkg.mod:

 MYPYPATH=src mypy --namespace-packages --explicit-package-bases .

Pitch

This option is needed to circumvent the Duplicate module names. I want to treat everything as a module also if technically the name is not consistent with a python module. Could we make that more agnostic?

Start with the module-mapping documentation linked in the issue and reproduce the shown MYPYPATH/mypy command using a namespace-pkg directory. Determine how a flag such as allow_all_module_names should affect hyphenated module names and the Duplicate module names case. Done should include an agreed option behavior and coverage for the documented example.