Built-in keywords on dataclasses

還沒有人認領這個 Issue。

* **Editor name and version**: VS Code July 1.48.1 (latest)
* **Platform**: OS X
* **Color scheme**: One Dark Pro
* **MagicPython version**: VS Code's version
* **5-10 lines of surrounding code**:
```
@dataclass
class SkipListNode(Generic[KT, VT]):
key: KT
value: VT
next: List[SkipListNode[KT, VT]] = field(default_factory=list)
```
* **A screenshot**:

In the screenshot, next is highlighted as a keyword. However, I don't believe that it should be, as it will only ever be accessed as `self.next` or `SkipListNode.next`.

使用報告中的 dataclass 程式碼片段在 VS Code 中重現語法醒目提示，然後追蹤將 dataclass 欄位名稱 `next` 標記為關鍵字的 Python 語法醒目提示規則。完成的標準是：在此情境中，`next` 不再被醒目提示為關鍵字，同時真正的 Python 關鍵字仍能正確地醒目提示。

由索引模型根據 Issue 內容生成。