fix(types): support union in CreationAttributes

[ephys]

Pull Request Checklist

• Have you added new tests to prevent regressions?
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Description Of Change

PR #13909 introduced a change where creation attributes that accept undefined were also as being optional in typings.

The way this change was implemented is incompatible with TS unions and broke with the following example #14129

closes #14129

I'm bringing this change in v6 only for backward compatibility. I will bring a different solution in v7, see #14091 (comment) for more

[WikiRik]

LGTM, can we also cherry-pick some other issues from the release log of v6 before we do the new release?

[ephys]

I'd prefer to do that in a separate PR but we can cancel the release of this one and merge the other one right afterwards (or just let both be published) :)

I'll do another small v7 PR that can be cherry-picked first, then open the cherry pick PR

[WikiRik]

Canceling the release and merging the other right afterward would have my preference

[ephys]

PR I'd like to merge and cherry-pick in v6 before merging this one: #14147

[snitin315]

Thank you so much.

[fzn0x]

Good to merge :)

[ephys]

This is going to cause an extra release but I'll merge this one because it's been 4 days and I haven't cherry-picked the other PRs yet, so might as well release this one while I work on the other ones

[github-actions]

🎉 This PR is included in version 6.16.3 🎉

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