Add OData header writing to ODataJsonOutputContext

[Copilot]

The new ODataUtf8JsonWriter-based serializer writes payloads but not OData headers (OData-Version, Content-Type). This works when using ODataMessageWriter (which writes headers first), but fails when ODataJsonOutputContext is created directly (e.g., in URI conversion utilities).

Changes

ODataMessageInfo

• Added optional internal Message property to carry message reference when header writing is needed

ODataMessageWriter

• Passes message reference to ODataMessageInfo when creating output context

ODataJsonOutputContext

• Writes OData-Version and Content-Type headers in constructor when message is available
• BuildContentTypeHeader() assembles Content-Type from media type, parameters, and charset
• Single-pass parameter iteration for charset detection
• Only executes when message provided (zero overhead for internal usage)

Example

// Direct creation now writes headers
var messageInfo = new ODataMessageInfo
{
    Message = message,  // Optional - enables header writing
    MediaType = new ODataMediaType("application", "json"),
    // ...
};

var context = new ODataJsonOutputContext(messageInfo, settings);
// Headers automatically written: OData-Version: 4.0, Content-Type: application/json;charset=utf-8

Backward compatible - existing code paths unaffected.

Original prompt

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This section details on the original issue you should resolve

<issue_title>New OData serializer does not write OData headers</issue_title>
<issue_description>

The OData serializer should write OData-specific headers based on the configuration it uses to write the request/response. For example: The OData version, the content-type, e.g:

OData-Version: 4.0
Content-Type: application/json;odata.metadata=minimal;odata.streaming=true;IEEE754Compatible=false;charset=utf-8

The ODataMessageWriter accepts a IODataRequest/ResponseMessage which wraps both the stream and the headers collection. It uses this wrapper to read and write headers when appropriate. The new serializer should provide a similar mechanism. But we should avoid unnecessary allocations, especially per-request allocations.

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🔹 Thanks for taking the time to suggest this feature! We appreciate your contributions. 🙌
</issue_description>

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

• Fixes New OData serializer does not write OData headers #3398

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