De-prioritise Dimname and DimnameList in python overload resolution (#51350)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/51350
`None` being a valid `Dimname` is awkward for optional `dim` arguments, as found
on NumPy's reduction functions like `std` and `var`. In these cases `dim=None`
should mean an all-reduction, but instead you get an error
"Please look up dimensions by name".
I've also had to fix `FunctionParameter::check` to actually check the first
element of `INT_LIST` arguments and reject non-int types. Otherwise, the dim
names end up calling the `int[]` overload and fail.
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D26756208
Pulled By: mruberry
fbshipit-source-id: 44221ca0f4822ec2c1f62b092466fd4f779eb45a
