Allow document transformers to access operation descriptions (#61264)

[vvimjam]

Allow document transformers to access operation descriptions

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Summary of the changes (Less than 80 chars)

Description

"Added an OperationDescriptions to OpenApiDocumentTransformerContext to allow document transformers to access endpoint metadata."

Fixes #61264

• OpenApiDocumentTransformerContext: Added OperationDescriptions property (IReadOnlyDictionary) to provide direct access to the C# metadata (attributes) for each operation.
• OpenApiDocumentService: Captured the mapping during the generation of paths and operations and passed it to the transformer execution context.
• PublicAPI.Unshipped.txt: Updated the public API definitions to include the new property.

[Copilot]

Pull request overview

This PR adds an OperationDescriptions property to OpenApiDocumentTransformerContext, enabling document transformers to access the mapping between OpenApiOperation instances and their ApiDescription metadata. This addresses the scenario where users need to inspect endpoint metadata (e.g., [AllowAnonymous]) during document-level transformations.

Changes:

• Added a new OperationDescriptions property (IReadOnlyDictionary<OpenApiOperation, ApiDescription>) to OpenApiDocumentTransformerContext.
• Plumbed a Dictionary<OpenApiOperation, ApiDescription> through GetOpenApiPathsAsync and GetOperationsAsync in OpenApiDocumentService to populate the mapping.
• Added two tests verifying that document transformers can access operation descriptions and endpoint metadata.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/OpenApi/src/Transformers/OpenApiDocumentTransformerContext.cs	New OperationDescriptions public property
src/OpenApi/src/Services/OpenApiDocumentService.cs	Populates and passes the operation-to-description dictionary
src/OpenApi/test/.../DocumentTransformerTests.cs	Two new tests for the feature

[vvimjam]

@dotnet-policy-service agree

[dotnet-policy-service]

Looks like this PR hasn't been active for some time and the codebase could have been changed in the meantime.
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