feat(models): add shared Content interface

[mdaneri]

Pull Request

Description

Introduce a shared abstraction for OpenAPI elements that expose a Content map, enabling generic helpers and reducing duplication across the model surface.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe):

Related Issue(s)

Fixes #2677

Changes Made

• Added IOpenApiContentElement / IOpenApiReadOnlyContentElement to represent the shared Content capability
• Updated IOpenApiResponse, IOpenApiRequestBody, IOpenApiParameter, and IOpenApiHeader to inherit the shared interface
• Updated corresponding model classes to implement the writable interface

Testing

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• All existing tests pass

Checklist

• My code follows the code style of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Versions applicability

• My change applies to the version 1.X of the library, if so PR link:
• My change applies to the version 2.X of the library, if so PR link:
• My change applies to the version 3.X of the library, if so PR link:
• I have evaluated the applicability of my change against the other versions above.

Additional Notes

None

[baywet]

Thanks for the contribution!
A couple of minor suggestions

[mdaneri]

@baywet I'm sure that you already know but the tests are failing on Windows due to differences in newline formats, specifically between CRLF and LF

[baywet]

Thank you for making the changes!

[baywet]

@mdaneri do you mean the unit tests? or a formatting issue with the source code?

[mdaneri]

@mdaneri do you mean the unit tests? or a formatting issue with the source code?

xunit tests 5 of 6 of them are failing on windows

[mdaneri]

for example,

Assert.Equal() Failure: Strings differ
                         ↓ (pos 14)
Expected: "swagger: '2.0'\ninfo:\n  version: 1.0.0\npat"···
Actual:   "swagger: '2.0'\r\ninfo:\r\n  version: 1.0.0\r\n"···
                         ↑ (pos 14)
at Microsoft.OpenApi.Tests.Models.OpenApiDocumentTests.SerializeSimpleDocumentWithTopLevelReferencingComponentsAsYamlV2Works() (file:///c%3A/Users/m_dan/Documents/GitHub/kestrun/OpenAPI.NET/test/Microsoft.OpenApi.Tests/Models/OpenApiDocumentTests.cs#L1466,0)

[mdaneri]

I think it's an issue with my environment I force windows to use \n only not \r\n

[baywet]

@mdaneri the public API export needs to be refreshed, would you mind pushing that latest change please?