Syntax highlighting issue when @ appears as first character after line continuation when indexing is present

還沒有人認領這個 Issue。

* **Editor name and version**: VS Code 1.71
* **Platform**: Any
* **Color scheme**: NA
* **MagicPython version**:
* **A sreenshot**:
I would expect syntax highlighting to be the same irrespective of whether the line is broken before or after the @ operator.

* **5-10 lines of surrounding code**:
```python
# Define variables so pylance doesn't complain.
long_variable_name = other_long_variable_name = 1

long_variable_name \
@ other_long_variable_name['some_index']

long_variable_name @ \
other_long_variable_name['some_index']
```

Originally from @tillahoffmann in https://github.com/microsoft/vscode/issues/161435

在受支援的編輯器中重現回報的 Python 程式碼片段，比較行延續出現在 @ 之前和之後、且後面接著索引表達式時的醒目提示效果。追蹤行延續和 @ 表達式的語法醒目提示文法進入點；完成條件是兩種等價形式都獲得相同的醒目提示效果。

由索引模型根據 Issue 內容生成。