Bug: form submit event does not expose event.submitter

[stefanprobst]

a form submit event provides an event.submitter property, which can be passed to new FormData(event.currentTarget, event.submitter).

currently, react's FormEvent<HTMLFormElement> does not expose event.submitter - it can only be accessed via (event.nativeEvent as SubmitEvent).submitter.

React version: 19.1

Steps To Reproduce

Link to code example: https://github.com/stefanprobst/issue-react-form-event-submitter

1. clone above repo, pnpm install && pnpm run dev
2. click the submit button, and see that the nativeEvent has a submitter property, while the react synthetic event does not

The current behavior

the submit event does not have a submitter property

The expected behavior

the submit event's submitter property references the submit button (like the native SubmitEvent does)