treat a package as if it had py.typed

[davidism]

I would like to be able to force mypy to look at the types provided by a package even if it does not provide a py.typed file. I've found that some packages I use have added good type annotations, but didn't realize they needed to provide a py.typed file as well. Some of these packages are only lightly maintained, so they may not get a new release with the file included any time soon.

mypy will ignore typing if py.typed isn't present, but it seems like that's something that should be overridable, just like you can tell mypy to ignore_missing_imports if a package doesn't have typing. I suggest a corresponding configuration such as assume_typed_imports.

An example of such a package is inflect. I opened an issue jaraco/inflect#133 and PR jaraco/inflect#135 to add the file, but it hasn't received attention. I have to add ignore_missing_imports currently.

[ethanhs]

I believe this is a duplicate of #8545.