Adding a test.

…ime lists

Even though using `Vpc.fromVpcAttributes()` using deploy-time lists like
from `Fn.importValue()`s and `CfnParameters` was never really supposed
to work, it accidentally did.

The reason for that is:

```ts

// Encoded list token
const subnetIds = Token.asList(Fn.importValue('someValue'))
// [ '#{Token[1234]}' ]

// Gets parsed to a singleton `Subnet` list:
const subnets = subnetIds.map(s => Subnet.fromSubnetAttributes({ subnetId: s }));
// [ Subnet({ subnetId: '#{Token[1234]}' }) ]

// This 'subnetId' is illegal by itself, and if yould try to use it for,
// say, an ec2.Instance it would fail. However, if you treat this single
// subnet as a GROUP of subnets:
new CfnAutoScalingGroup({ subnetIds: subnets.map(s => s.subnetId) })
// [ '#{Token[1234]}' ]

// And this resolves back to:
resolve(cfnSubnetIds)
// SubnetIds: { Fn::ImportValue: 'someValue' }
```

--------

We introduced an additional check in #11899 to make sure that the
list-element token that represents an encoded list (`'#{Token[1234]}'`)
never occurs in a non-list context, because it's illegal there.

However, because:

* `Subnet.fromSubnetAttributes()` logs the subnetId as a *warning*
  to its own metadata (which will log a string like `"there's something
  wrong with '#{Token[1234]}' ..."`).
* All metadata is resolved just the same as the template expressions
  are.

The `resolve()` function encounters that orphaned list token in the
metadata and throws.

--------

The *proper* solution would be to handle unparseable list tokens
specially to never get into this situation, but doing that requires
introducing classes and new concepts that will be a large effort and
not be backwards compatible. Tracking in #4118.

Another possible solution is to stop resolving metadata. I don't
know if we usefully use this feature; I think we don't. However,
we have tests enforcing that it is being done, and I'm scared
to break something there.

The quick solution around this for now is to have
`Subnet.fromSubnetAttributes()` recognize when it's about to log
a problematic identifier to metadata, and don't do it.

Fixes #11945.