Do not diagnose no-self-use or unused-argument for methods of generic structural types (Protocol[T])

[jmehnle]

This is a follow-up to #3002, which addressed the basic issue, but there's a special case that is still broken: when a protocol class is a generic, i.e., it inherits not simply from Protocol but from Protocol[T] or some other generic form of Protocol.

Steps to reproduce

import typing_extensions as tex
from typing import TypeVar

T = TypeVar("T")

@tex.runtime
class Hasher(tex.Protocol[T]):
    """A hashing algorithm, e.g. :func:`hashlib.sha256`."""
    def update(self, bs: bytes):
        ...
    def digest(self) -> bytes:
        ...

Current behavior

************* Module pylinttest
pylinttest.py:9:21: W0613: Unused argument 'bs' (unused-argument)
pylinttest.py:9:4: R0201: Method could be a function (no-self-use)
pylinttest.py:11:4: R0201: Method could be a function (no-self-use)
pylinttest.py:2:0: C0411: standard import "from typing import TypeVar" should be placed before "import typing_extensions as tex" (wrong-import-order)

Expected behavior

No diagnostics.

pylint --version output

pylint 2.6.0
astroid 2.4.2
Python 3.7.9 (default, Sep  6 2020, 13:20:25)
[Clang 11.0.3 (clang-1103.0.32.62)]

[hippo91]

@jmehnle thanks for the report. It makes sense and i can reproduce it.