[Bug] Class method 'self' looses special self scope with added type annotation

還沒有人認領這個 Issue。

Got send here from 'vscode-python' https://github.com/microsoft/vscode-python/issues/11593

* **Editor name and version**: VS Code version: 1.44.2
* **Platform**: Windows_NT x64 10.0.17134
* **Color scheme**: Custom (close to Monokai)
* **MagicPython version**: Dunno which vscode uses

Without type annotation everything is just fine.

When a type annotation is added to the `self` parameter the special scope for `self` is missing.

## Steps to reproduce:

Paste the following code into a *.py file and inspect the `self` parameter with the developer token inspect tool. Like in the screenshots above.
The `self` parameter of the `bad_func` should show the actual scopes and the `self` parameter of the `good_func` should show the expected scopes.
```
class Test:
def bad_func(self: Test):
pass

def good_func(self):
pass
```

從重現的 Python 程式碼片段開始，使用開發者 token 檢查工具檢查有註解和無註解的 self 參數的 token 範圍。追蹤處理類別方法參數的語法醒目提示路徑；當 self: Test 保留與未註解的 self 相同的特殊 self 範圍時，即表示完成。

由索引模型根據 Issue 內容生成。