Refactor Field components with const arrow functions (#1261)

## Summary
- convert all remaining Field components to const arrow functions
- document the refactor in the CHANGELOG

## Testing
- `npm run lint`
- `npm run build`


------
https://chatgpt.com/codex/tasks/task_e_68684db1b6b88331837307a54e3f9dc1

src/components/FieldEnum.tsx

@@ -1,4 +1,3 @@
-import React from 'react'
 import InputEnum, {InputEnumProps} from './InputEnum'
 import Fieldset from './Fieldset';
 
@@ -11,10 +10,12 @@ type FieldEnumProps = InputEnumProps & {
 };
 
 
-export default class FieldEnum extends React.Component<FieldEnumProps> {
-  render() {
-    return <Fieldset label={this.props.label} fieldSpec={this.props.fieldSpec}>
-      <InputEnum {...this.props} />
+const FieldEnum: React.FC<FieldEnumProps> = (props) => {
+  return (
+    <Fieldset label={props.label} fieldSpec={props.fieldSpec}>
+      <InputEnum {...props} />
     </Fieldset>
-  }
-}
+  );
+};
+
+export default FieldEnum;