feat: Microsoft.OpenApi v2.x (OpenAPI v3.1 Support) and .NET 10

[sergey-tihon]

• OpenApi v2 migtarion guide - https://github.com/microsoft/OpenAPI.NET/blob/main/docs/upgrade-guide-2.md
• I think that we need new Swashbuckle to fix tests - Plans on official support for OpenApi 3.1.0 domaindrivendev/Swashbuckle.AspNetCore#2349

[Copilot]

Pull Request Overview

This PR upgrades Microsoft.OpenApi from v2.x to v2.3.0 to add OpenAPI v3.1 support, removing the separate Microsoft.OpenApi.Readers dependency and updating various dependencies.

Key changes:

• Updated OpenAPI library dependencies and added OpenAPI v3.1 support
• Refactored code to use new OpenAPI library interfaces and APIs
• Modernized F# syntax with abbreviated lambda expressions

Reviewed Changes

Copilot reviewed 17 out of 18 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
paket.dependencies	Updated FSharp.Core, System.Text.Json, and OpenAPI packages; added Swashbuckle preview
src/SwaggerProvider.DesignTime/v3/DefinitionCompiler.fs	Adapted to new IOpenApiSchema interface and JsonSchemaType enum
src/SwaggerProvider.DesignTime/v3/OperationCompiler.fs	Updated to use IOpenApiPathItem and IOpenApiParameter interfaces
tests/Swashbuckle.WebApi.Server/Startup.fs	Replaced SerializeAsV2 with OpenApiVersion property
tests/SwaggerProvider.Tests/Schema.Parser.Tests.fs	Updated OpenAPI document parsing to use new API
src/SwaggerProvider.DesignTime/Provider.OpenApiClient.fs	Updated schema reading to use new OpenAPI parsing methods
Multiple files	Applied F# syntax modernization and version updates

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[Copilot]

The code accesses schemaObj.AllOf.[0] without null checking schemaObj.AllOf first. While there's a count check, if schemaObj.AllOf is null, Count property access will throw a NullReferenceException.

[Copilot]

Pull request overview

Copilot reviewed 28 out of 29 changed files in this pull request and generated 6 comments.

Comments suppressed due to low confidence (1)

tests/SwaggerProvider.Tests/Schema.Parser.Tests.fs:36

• The diagnostic error checking code is commented out (lines 32-36). If the diagnostic errors are no longer being checked after the migration to OpenApi v2.x, this could lead to silent parsing failures. Either remove the commented code if it's no longer needed, or provide an explanation for why error checking has been disabled. If the API for checking diagnostics has changed, update the code to use the new API.

        (*        if diagnostic.Errors.Count > 0 then
               failwithf "Schema parse errors:\n- %s"
                   (diagnostic.Errors
                    |> Seq.map (fun e -> e.Message)
                    |> String.concat ";\n- ")*)

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[Copilot]

The comment states "Swashbuckle doesn't generate 'additionalProperties' in Swagger 2.0 for dictionaries". However, if the tests have been removed due to a known limitation in the test server setup rather than an actual issue in SwaggerProvider itself, this should be made clearer. Consider adding information about whether this is a temporary workaround and if there's a plan to re-enable these tests once Swashbuckle is fixed, or if this represents a permanent limitation.

Suggested change

	// NOTE: Dictionary tests removed because Swashbuckle doesn't generate 'additionalProperties' in Swagger 2.0 for dictionaries
	// The swagger.json produces: {"type": "object"} instead of {"type": "object", "additionalProperties": {"$ref": "#/definitions/PointClass"}}
	// The corresponding OpenAPI 3.0 tests in v3/Swashbuckle.ReturnControllers.Tests.fs cover this functionality
	// See: tests/SwaggerProvider.ProviderTests/v3/Swashbuckle.ReturnControllers.Tests.fs for working dictionary tests
	// NOTE: Dictionary tests for the Swagger 2.0 endpoint are disabled here because the Swashbuckle test server
	// (and its Swagger 2.0 generator) does not emit 'additionalProperties' for dictionary types.
	// The generated swagger.json currently contains: {"type": "object"} instead of
	// {"type": "object", "additionalProperties": {"$ref": "#/definitions/PointClass"}}.
	// This is a limitation of the Swashbuckle/Swagger 2.0 test setup, not of SwaggerProvider itself.
	// The corresponding OpenAPI 3.0 tests in v3/Swashbuckle.ReturnControllers.Tests.fs validate dictionary support.
	// See: tests/SwaggerProvider.ProviderTests/v3/Swashbuckle.ReturnControllers.Tests.fs for working dictionary tests.
	// If Swashbuckle's Swagger 2.0 generator is ever updated to emit 'additionalProperties' correctly,
	// these v2 dictionary-return tests can be re-enabled.