General issue - `py/not-named-cls` should trigger for implicit class methods

**Description of the issue**

`py/not-named-cls` should trigger for wrong first arg name for special method names that implicitly make the methods class methods.
For example:
```py
class Example:
def __init_subclass__(self): # should error and say to use `cls` instead
pass

def __class_getitem__(self): # should error and say to use `cls` instead
pass
```