`StrOrBytesPath | FileDescriptor` alias

[Avasam]

Opening an issue so we don't forget.

Original comment from @AlexWaygood :

We could actually consider adding this alias to _typeshed; there's a bunch of functions in os/__init__.pyi that could use it. os/__init__.pyi currently defines an _FdOrAnyPath alias. We don't need to add the alias to _typeshed in this PR, though.

There's a handful of _OpenFile aliases also defined in multiple stubs

There's also a lot of int | StrOrBytesPath, StrOrBytesPath | int and StrOrBytesPath | FileDescriptor which could be replaced by the alias.

[Avasam]

With a new mypy release around the corner, adding helper types before mypy updates its vendored typeshed might be a good idea.

[AlexWaygood]

There don't seem to be any objections :)

The only reservation I have is about the name. OpenFile isn't very descriptive/accurate, since for the StrOrBytesPath half of the alias, the file hasn't actually been opened yet. Maybe something like FileDescriptorOrPath?

[JelleZijlstra]

I would be okay with PathOrFD since "FD" for "file descriptor" is pretty commonly understood, but maybe it's still too obscure.

[hauntsaninja]

"fd" seems fine; it's commonly used as an identifier in the Python docs and e.g. os.fdopen is a thing

[AlexWaygood]

I'd still lean towards FileDescriptorOrPath, but happy with either!