aws-cdk: (core): `Vpc.fromVpcAttributes` using list tokens now throws errors

When importing a VPC using outputs from another stack, if the route table IDs are not specified for each imported subnet, a warning is printed to the console, as expected:

No routeTableId was provided to the subnet '#{Token[TOKEN.58]}'. Attempting to read its .routeTable.routeTableId will return null/undefined. (More info: https://github.com/aws/aws-cdk/pull/3171)

This warning line is wrongly evaluated by the new “floating token” check introduced by #11899, and throws an error when synthesizing the stack:

Found an encoded list token string in a scalar string context. Use 'Fn.select(0, list)' (not 'list[0]') to extract elements from token lists.

Additionally, this line is “consumed” by the floating-token check and does not reach the console.

Reproduction Steps

import * as cdk from "@aws-cdk/core";
import * as ec2 from "@aws-cdk/aws-ec2";

class TestStack extends cdk.Stack {
  constructor(scope: cdk.App, id: string, props: cdk.StackProps) {
    super(scope, id, props);

    const vpcId = cdk.Fn.importValue("myVpcId");
    const availabilityZones = cdk.Fn.split(",", cdk.Fn.importValue("myAvailabilityZones"));
    const publicSubnetIds = cdk.Fn.split(",", cdk.Fn.importValue("myPublicSubnetIds"));

    ec2.Vpc.fromVpcAttributes(this, "importedVpc", {
      vpcId,
      availabilityZones,
      publicSubnetIds,
    });
  }
}

const app = new cdk.App();
new TestStack(app, "TestStack", {});

What did you expect to happen?

VPC is imported without error, and the following warning line is printed to the console:

No routeTableId was provided to the subnet '#{Token[TOKEN.58]}'. Attempting to read its .routeTable.routeTableId will return null/undefined. (More info: https://github.com/aws/aws-cdk/pull/3171)

What actually happened?

No warning is printed about the route table, and the stack fails to synthesize with the following error:

Found an encoded list token string in a scalar string context. Use 'Fn.select(0, list)' (not 'list[0]') to extract elements from token lists.

Environment

• CDK CLI Version : 1.77.0
• Framework Version: 1.77.0
• Node.js Version: 12.20.0
• OS : Linux (Pop!_OS 20.04 LTS x86_64)
• Language (Version): TypeScript 3.9.7

Other

The floating token check should ignore CDK “logging” lines if possible.

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This is 🐛 Bug Report