doc: document "flat" `util.inspect` signature

[refack]

The code allows calling it as

util.inspect(object, [showHidden], [depth], [colors])

It wash refactored 6 years ago (Refs: 07774e6) and marked legacy, but it seems it is still often used, and so should be documented.

Hi i'm still new and i would like to contribute, do i add in the docs that you could also use the signature util.inspect(object, [showHidden], [depth], [colors]) aside from the new one?

[BridgeAR]

I don't think that it is a good API signature and documenting it would go in the wrong direction.

[refack]

I don't think that it is a good API signature and documenting it would go in the wrong direction.

I think we should either deprecate or document.
From #22753 and #22751 it seems like there is no consensus for deprecation, so IMHO we need to document this.