Add OpenApiXmlNodeType enum and update OpenApiXml for OAI 3.2.0 support

[Copilot]

Overview

This PR implements the XML Object updates specified in OpenAPI 3.2.0 specification, introducing a new NodeType property while maintaining backward compatibility with earlier OpenAPI versions.

Changes

New Functionality

• Added OpenApiXmlNodeType enum with five values:

  • Element - represents XML element nodes
  • Attribute - represents XML attribute nodes
  • Text - represents text nodes
  • Cdata - represents CDATA sections
  • None - represents no specific node type

• Added NodeType property to OpenApiXml class for explicit XML node type specification

Backward Compatibility

The existing Attribute and Wrapped boolean properties are now marked as obsolete but remain fully functional:

• Attribute property (obsolete):

  • Getter returns true when NodeType == OpenApiXmlNodeType.Attribute
  • Setter sets NodeType to Attribute when true, None when false

• Wrapped property (obsolete):

  • Getter returns true when NodeType == OpenApiXmlNodeType.Element
  • Setter sets NodeType to Element when true, None when false

Version-Specific Serialization

The serialization behavior now depends on the OpenAPI specification version:

OpenAPI 3.2.0 and above:

{
  "name": "item",
  "nodeType": "element"
}

OpenAPI 3.1.0 and below:

{
  "name": "item",
  "wrapped": true
}

This ensures documents remain compatible with their target specification version.

Deserialization Support

All deserializers (V2, V3, V3.1, V32) have been updated:

• V32 deserializer now handles the nodeType field
• Earlier version deserializers continue to support attribute and wrapped fields
• Both old and new properties can be read, ensuring forward and backward compatibility

Testing

• Added 5 new tests covering NodeType serialization in different OpenAPI versions
• All existing 1,364 tests continue to pass
• Public API file updated to reflect the new enum and obsolete attributes

Example Usage

// New approach (OpenAPI 3.2.0+)
var xml = new OpenApiXml
{
    Name = "pet",
    NodeType = OpenApiXmlNodeType.Element
};

// Legacy approach (still works, but marked obsolete)
#pragma warning disable CS0618
var xml = new OpenApiXml
{
    Name = "attr",
    Attribute = true
};
#pragma warning restore CS0618

Fixes microsoft#89

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Original prompt

---

This section details on the original issue you should resolve

<issue_title>xmlObject fields updates</issue_title>
<issue_description>OAI 3.2.0 makes a few updates to the XML object

• Add a new enum named OpenApiXmlNodeType (element, attribute, text, cdata, or none)
• Add a new property called NodeType
• Mark the Attribute property as obsolete
• Make the Attribute property getter evaluate whether the NodeType property is set to attribute
• Make the Attribute property setter set the NodeType property to attribute when true, none when false
• DO NOT serialize the attribute property in 3.2.0, but serialize it in 3.1.0
• Mark the Wrapped property as obsolete
• Make the Wrapped property getter evaluate whether NodeType is set to element
• Make the Wrapped property setter set the NodeType property to element when true, none when false
• DO NOT serialize the wrapped property in 3.2.0, but serialize it in 3.1.0
• DO NOT serialize the NodeType property in 3.1.0 or below.</issue_description>

<agent_instructions>make sure you update the public api export</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #11

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