Describe the bug
When using Semantic Kernel sampling via MCP, the internal payload passed from Semantic Kernel to MCP contains a dictionary whose values may include anonymous types (objects generated by Semantic Kernel and not controllable by the application).

In ModelContextProtocol 0.5.0-preview.1, calling
ModelContextProtocol.AIContentExtensions.ToJsonObject(IReadOnlyDictionary<string, object?> properties)
throws a System.NotSupportedException when any dictionary value is an anonymous type.

This previously worked in 0.4.0-preview.3 (stdio transport only) but now fails in 0.5.0-preview.1, including stdio, indicating that stdio and web transports now share the same serialization pipeline.

To Reproduce
Use Semantic Kernel with MCP sampling (AddSamplingChatClient)

Trigger a prompt invocation where Semantic Kernel generates arguments/metadata internally

Ensure the dictionary passed into
ModelContextProtocol.AIContentExtensions.ToJsonObject(...)
contains any anonymous type as a value (structure does not matter)

Run with ModelContextProtocol 0.5.0-preview.1

Observe serialization failure

Minimal conceptual example:

var dict = new Dictionary<string, object?>
{
["data"] = new { X = 1.0, Y = 2.0 }
};

AIContentExtensions.ToJsonObject(dict);

Expected behavior
ToJsonObject should be able to serialize dictionaries whose values are anonymous types, producing a valid JsonObject / JsonNode.

At minimum, anonymous types should be handled as plain object graphs rather than requiring source-generated JsonTypeInfo, which cannot be provided for anonymous types.

This is especially important because:

These anonymous types are generated internally by Semantic Kernel

Application developers cannot intercept or replace them

Logs

System.NotSupportedException: JsonTypeInfo metadata for type
'<>f__AnonymousType0`5[...]' was not provided by TypeInfoResolver
of type 'ModelContextProtocol.McpJsonUtilities+JsonContext'
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException_NoMetadataForType
   at System.Text.Json.JsonSerializer.SerializeToNode
   at ModelContextProtocol.AIContentExtensions.ToJsonObject
   at ModelContextProtocol.Server.McpServer.SampleAsync(...)

Additional context

In 0.4.0-preview.3:

stdio transport worked

web transport failed (likely due to different serialization pipelines)

In 0.5.0-preview.1:

Both stdio and web transports fail

Indicates a unified pipeline that now enforces the same resolver behavior

Request / suggestion:
Enhance ModelContextProtocol.AIContentExtensions.ToJsonObject to support
dictionary values containing anonymous types, either by:

Falling back to a non–source-generated resolver for such values, or

Detecting anonymous types and serializing them via a compatible JsonSerializerOptions

This would restore compatibility with Semantic Kernel sampling scenarios
where developers cannot control the generated object shapes.