[OpenAPI] Validate OpenAPI documents

[martincostello]

Validate OpenAPI documents

Validate OpenAPI documents generated in tests for validity.

Description

To see if I could flush out the errors for #63090 with Microsoft.OpenApi's built-in validation (it doesn't find them) I spotted a few other validation errors that are. This fixes them and adds some tests that validate the generated documents using the default ruleset.

• Validate OpenAPI documents with Microsoft.OpenApi.
• Exclude HTTP QUERY endpoints as they are not valid in OpenAPI 3.1 (added by [OpenApi] Ignore unknown HTTP methods #63034).
• Fix incorrect parameter casing validation warnings.

Relates to #63090.

[Copilot]

Pull Request Overview

This PR validates OpenAPI documents generated in tests for validity using Microsoft.OpenApi's built-in validation to help identify and fix validation errors. The primary goal is to ensure generated OpenAPI documents conform to OpenAPI specifications.

• Adds validation tests to verify generated OpenAPI documents are valid
• Fixes parameter naming issues and excludes unsupported HTTP QUERY method
• Updates test snapshots to reflect the corrected parameter casing

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

File	Description
OpenApiDocumentIntegrationTests.cs	Adds new validation test method and refactors document retrieval into helper method
ApiDescriptionExtensions.cs	Excludes HTTP QUERY method from OpenAPI generation as it's not supported in OpenAPI 3.1
TestController.cs	Fixes parameter naming by adding explicit Name attributes to FromRoute parameters
Three snapshot files	Updates test snapshots to reflect corrected parameter names and removal of QUERY endpoints

[captainsafia]

LGTTM -- some small nits. Thanks!

[martincostello]

Looks like a flaky SignalR test.

[BrennanConroy]

Looks like a flaky SignalR test.

I think #63278 should fix that

[captainsafia]

/ba-g Unrelated flakey test.