demo-general的选择器配置表达式后无法自定义key

## **Describe the bug (required)** / **详细描述 bug（必填）**
demo-general的选择器配置表达式后无法自定义key, 只能填官方默认的lable和value, 比如后端返回的是code和name这种就不能直接配置, 仍需要在代码里转一下,如过表达式支持自定义lable和value会方便很多

Start by reproducing the selector configuration expression problem in demo-general with backend fields named code and name instead of the default label and value. Trace how the expression maps selector options, then verify that custom keys can be configured without converting the response in application code. Confirm the behavior with a focused regression test if the existing test setup covers this configuration.

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