Show the errors of an AggregateError behind a cause (#97830)
A failed `fetch` hid the reason of the failure. Node.js reports every
refused connection attempt in the `errors` of an `AggregateError`, and
the terminal logged `[errors]: [ [Error], [Error] ]` without the address
or the port of a single attempt.
An `AggregateError` keeps its errors in an array. Node.js spends one
level of the inspect depth on that array, and one more level on each
error in the array, while a `cause` costs one level only. The errors of
an `AggregateError` behind a cause therefore fell outside the default
depth of two. Node.js also returns an error early when it carries no own
properties, before it applies the depth, so the collapse hit only the
errors that carry diagnostics.
Next.js now adds the missing level back for an `AggregateError`, so its
errors print at the same nesting as a cause. A depth of `null` means
unlimited and stays unchanged, because `null + 1` would reduce it to one
level.
