Wrap with Obx removes variables from string interpolation

When I wrap the following widget with Obx, it modifies the code
```dart
FocusTraversalOrder(
    order: LexicalFocusOrder('$colIdx'),
    child: Container(),
)
```
becomes 
```dart
Obx(() => FocusTraversalOrder(
      order: LexicalFocusOrder(''),
      child: Container(),
)),
```