fix(core): throw on intrinsics in CFN update and create policies

[comcalvi]

Issue # (if applicable)

Closes #27578, Closes #30740.

Reason for this change

cfn-include only allows Intrinsics in resource update and create policies to wrap primitive values. If Intrinsics are included anywhere else, cfn-include silently drops them.

CDK's type system does not allow intrinsics in resource policies unless they define a primitive value. cfn-include adheres to this type system and drops any resource policies that use an intrinsic to define a complex value. This is an example of a forbidden use of intrinsics:

  "Resources": {
    "ResourceSignalIntrinsic": {
     // ....
      "CreationPolicy": {
        "ResourceSignal": {
          "Fn::If": [
            "UseCountParameter",
            {
              "Count": { "Ref": "CountParameter" }
            },
            5
          ]
        }
      }
    }
  }
}

This is forbidden because an intrinsic contains the Count property of this policy. CFN allows this, but CDK's type system does not permit it.

Description of changes

cfn-include will throw if any intrinsics break the type system, instead of silently dropping them.

CDK's type system is a useful constraint around these resource update / create policies because it allows constructs that modify them, like autoscaling, to not be token-aware. Tokens are not resolved at synthesis time, so it makes it impossible to modify these with simple arithmetic if they contain tokens.

The CDK will never (or at least should not) generate a token that breaks this type system.

Thus, the only use-case for allowing these tokens is cfn-include. Supporting these customers would require the CDK type system to allow these, and thus CDK L2s should handle such cases; except, for L2 customers, this use-case does not happen. Explicitly reject templates that don't conform to this.

Throwing here is a breaking change, so this is under a feature flag.

Additionally add a new property, dehydratedResources -- a list of logical IDs that cfn-include will not parse. Those resources still exist in the final template.

This does not impact L2 users.

Description of how you validated changes

Unit testing.

Manually verified that this does not impact any L2s.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

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• Commit ID: 6545b91
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