feat: expose submitter to use:enhance SubmitFunction

[msonnb]

closes #9414

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[dummdidumm]

Thank you!

[igneosaur]

Hi you two, you might have seen I've opened up an issue and a PR that references this PR. It looks like the SubmitFunction type is duplicated in index.d.ts (due to some TS bug it seems) which is the type that is accessed from any submit function declaration inside a SvelteKit app (rather than the enhance prop on a form). This new PR just adds the submitter argument to this additional type.

Thanks for this feature!