chore(spec2cdk): handle undefined properties in the reference interfaces

[leonmk-aws]

Issue # (if applicable)

Closes #.

Reason for this change

When a ref interface property is optional (e.g. workteamName?: string), the generated constructor code that extracts values from ref objects via optional chaining (?.ref?.property) would cause a compile time error.

Description of changes

• Added getRefProperty utility that extracts a property from a ref object and throws a TypeError if the ref exists but the target property is undefined. Returns undefined when the ref itself is null, allowing ?? fallback chains to work naturally.

• Added overloads to ensureStringOrUndefined so TypeScript correctly narrows the return type:

  • undefined input → returns undefined
  • {} input → returns string
  • {} | undefined input → returns string | undefined

Before

this.functionName = (props.functionName as IFunctionRef)?.functionRef?.functionName
  ?? cdk.ensureStringOrUndefined(props.functionName, "functionName", "lambda.IFunctionRef | string");

After

this.functionName = cdk.getRefProperty((props.functionName as IFunctionRef)?.functionRef, 'functionName')
  ?? cdk.ensureStringOrUndefined(props.functionName, "functionName", "lambda.IFunctionRef | string");

Description of how you validated changes

Added unit tests for the new function.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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

[aws-cdk-automation]

➡️ PR build request submitted to test-main-pipeline ⬅️

A maintainer must now check the pipeline and add the pr-linter/cli-integ-tested label once the pipeline succeeds.