FieldInfo `label` property is null for expression fields

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### Actual behavior

I'm migrating @arcgis/core/widgets/Feature/FeatureViewModel to @arcgis/core/popup/Feature.

The `fieldInfos` in content type FieldsContent with an expression field do not have a label.

@arcgis/core/widgets/Feature/FeatureViewModel

@arcgis/core/popup/Feature

### Expected behavior

FieldInfo with expression field should have a label.

### Reproduction sample

n/a

### Reproduction steps

n/a

### Reproduction browser

Edge 148 on Windows 11

### SDK version (check your console)

5.1.0-next.113

### Operating System (check https://whatsmyos.com)

Win 11