Exclude Fn::ForEach resources from Ref and GetAtt argument completions

[deepfuriya]

Summary

Filters out Fn::ForEach::* resources from autocomplete suggestions when inside !Ref and !GetAtt intrinsic functions. These loop construct resources are not valid references and should not appear as completion options.

Changes

• IntrinsicFunctionArgumentCompletionProvider.ts:
  • getResourceCompletions(): Skip resources with names starting with Fn::ForEach::
  • getGetAttResourceCompletions(): Skip resources with names starting with Fn::ForEach::

Testing

• Added unit tests in IntrinsicFunctionArgumentCompletionProvider.Ref.test.ts
• Added unit tests in IntrinsicFunctionArgumentCompletionProvider.GetAtt.test.ts
• Added e2e test in Completion.test.ts for YAML cross-reference completions

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