Add flatten property tests for unknown type and read-only properties

[Copilot]

Plan for adding flatten property tests

• Explore repository structure and understand existing flatten-property tests
• Add test case 1: Flatten property with unknown type
  • Add model with properties?: unknown field
  • Apply @Azure.ClientGenerator.Core.Legacy.flattenProperty decorator
  • Add PUT operation with scenario
  • Add mock API definition in mockapi.ts
• Add test case 2: Flatten property with all read-only properties
  • Add SolutionProperties model with all @visibility(Lifecycle.Read) fields
  • Add Solution model with required and optional flattened properties
  • Add operation with body parameter
  • Add mock API definition in mockapi.ts
• Build and validate the changes
  • Run build to compile TypeScript
  • Run validate-scenarios to ensure spec is valid
  • Run validate-mock-apis to ensure mock APIs are correct
• Address review feedback
  • Remove unused @azure-tools/typespec-azure-core import and using global.Azure.Core
• Request code review

Summary

Successfully added two new test cases and addressed review feedback to remove unnecessary imports.

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Spector] Add more tests for flatten property</issue_title>
<issue_description>Add two tests under packages/azure-http-specs/specs/azure/client-generator-core/flatten-property:

1. Flatten property case for an non-model type like unknown, typespec like this:

model XXX {
  #suppress "@azure-tools/typespec-azure-core/no-unknown" "FIXME: Update justification, follow aka.ms/tsp/conversion-fix for details"
  properties?: unknown;
}

@@Azure.ClientGenerator.Core.Legacy.flattenProperty(XXX.properties);

2. Flatten property case for all readOnly, typespec like this:

model SolutionProperties {
  @visibility(Lifecycle.Read)
  solutionId?: string;
  @visibility(Lifecycle.Read)
  title?: string;
  @visibility(Lifecycle.Read)
  content?: string;
}
model Solution{
  @Azure.ClientGenerator.Core.Legacy.flattenProperty
  properties: SolutionProperties;
  @Azure.ClientGenerator.Core.Legacy.flattenProperty
  propertiesOptional?: SolutionProperties;
}
op test(@body body:Solution):void;

/cc @MaryGao </issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Spector] Add more tests for flatten property #3711

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[v-jiaodi]

@copilot remove import "@azure-tools/typespec-azure-core" and using global.Azure.Core as it is not used.

[Copilot]

Done in commit 260bfdf. Removed the unused import and using statement - the Lifecycle enum is available without explicitly importing Azure.Core.