[field] Does not invalidate certain required controls

# Bug report

## Reproducible example

RadioGroup: https://codesandbox.io/p/sandbox/sweet-brattain-q9ptqr
Select: https://codesandbox.io/p/sandbox/eloquent-pond-cgnlg5

## Current behavior

```jsx

{/* the rest of the select */}

This field is required

```

When there is no initial value (e.g. no `defaultValue`/`value` or `defaultValue=""`) and the validation mode is `"onBlur"`, Tabbing through the controls without making any selection doesn't not trigger the error

## Expected behavior

Validate different types of empty values correctly

## Base UI version

master & `1.0.0-alpha.5`

## Additional context

Only tried Input, RadioGroup and Select so far