Support extensions for `info.contact` object in OpenAPI 3.1.0

[dani2819]

Current Behavior

When parsing an OpenAPI 3.1.0 document with extensions in the info.contact object, the library removes the extensions under info.contact. This results in loss of custom metadata that is intended to be retained for various use cases.

Expected Behavior

According to the OpenAPI 3.1.0 specification, it is valid to use extensions (properties starting with x-) within the info.contact object. The library should correctly parse and retain these extensions.

Example of a valid OpenAPI 3.1 document:

openapi: 3.1.0
info:
  title: Sample API
  version: 1.0.0
  contact:
    name: API Support
    x-custom-extension: "Custom Extension Value"
paths: {}

Steps to Reproduce

1. Create an OpenAPI 3.1.0 document that includes extensions within the info.contact object.
2. Use the library to parse the OpenAPI document.
3. Observe that the extensions are missing in the parsed output.

Example Code

package main

import (
    "github.com/pb33f/libopenapi"
    "os"
)

func main() {
    oasFile, _ := os.ReadFile("sample.yaml")
    document, _ := libopenapi.NewDocument(oasFile)
    document.BuildV3Model()
    b, _ := document.Render()
    _ = os.WriteFile("output.yaml", b, 0644)
}

The output.yaml does not contain x- properties under info.contact

Environment

• Library Version: [v0.16.10]
• OpenAPI Version: [3.1.0]
• Go Version: [1.23.0]
• Operating System: [macOS Sanoma 14.5]

[daveshanley]

This was fixed here: https://github.com/pb33f/libopenapi/commit/0200809765f7018b6fe4ee14cf6d148e77761f6e

This issue cannot be re-created anymore with libopenapi v0.18.1+