Closes #13638: document PyErr_SetFromErrnoWithFilenameObject,

PyErr_SetFromWindowsErrWithFilenameObject, and
PyErr_SetExcFromWindowsErrWithFilenameObject.

Note that PyErr_SetExcFromWindowsErrWithFilenameObjectAndSomeOtherParametersSoThatTheNameGetsSoLongThatNobodyIsEverGonnaUseThisStrangeFunctionForAnything is still undocumented.