register the user info and link account

register.tsx

 const user = useUser();

  const registerFormHandler = async ({ fullname, password }) => {
    if (user && user.phoneNumber) {
      const email = convertPhoneToEmail(user.phoneNumber);
      const credential = EmailAuthProvider.credential(email, password);
      const userCred = await linkWithCredential(user, credential);
      await updateProfile(userCred.user, {
        displayName: fullname,
      });
      await signOut(auth);
      registered();
    }
  };