Add CreateJson overloads to BinaryContent for simplified JSON serialization

[Copilot]

Summary

This PR adds two new CreateJson overloads to BinaryContent that simplify the common pattern of creating binary content from JSON-serializable objects.

Problem

Currently, creating BinaryContent from a JSON object requires a two-step process:

BinaryContent content = BinaryContent.Create(BinaryData.FromObjectAsJson(
    new {
        model = "gpt-4.1",
        prompt = new {
            id = "pmpt_abc123",
            version = "2",
            variables = new {
                customer_name = "Jane Doe",
                product = "40oz juice box"
            }
        }
    }
));

Solution

This PR introduces two new static factory methods that provide a more convenient API:

// Simple case with default serialization options
BinaryContent content = BinaryContent.CreateJson(
    new {
        model = "gpt-4.1",
        prompt = new {
            id = "pmpt_abc123",
            version = "2",
            variables = new {
                customer_name = "Jane Doe",
                product = "40oz juice box"
            }
        }
    }
);

// With custom JsonSerializerOptions
BinaryContent content = BinaryContent.CreateJson(obj, options);

// With JsonTypeInfo for AOT scenarios
BinaryContent content = BinaryContent.CreateJson(obj, jsonTypeInfo);

API Changes

Added two new public methods to BinaryContent:

public static BinaryContent CreateJson<T>(T jsonSerializable, JsonSerializerOptions? options = default)
public static BinaryContent CreateJson<T>(T jsonSerializable, JsonTypeInfo<T> jsonTypeInfo)

Implementation Details

• Uses existing BinaryData.FromObjectAsJson internally for consistent behavior
• Reuses the existing BinaryDataBinaryContent internal class
• Added proper XML documentation and pragma directives to handle linter rules
• Updated API surface files for both .NET Standard 2.0 and .NET 8.0
• Added comprehensive tests covering various scenarios

Testing

• All existing tests continue to pass (68/68)
• Added new tests for both overloads with different scenarios:
  • Basic JSON serialization
  • Custom JsonSerializerOptions
  • Verification that results match the existing pattern
  • Both sync and async operations

Fixes #50920

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[KrzysztofCwalina]

@copilot, continue working on this PR. I changed the credits

[Copilot]

@copilot, continue working on this PR. I changed the credits

Completed all requested changes including adding MediaType property and consolidating tests. All tests are passing. Commit 72e14a1

[KrzysztofCwalina]

@copilot, continue working on this

[Copilot]

lastly, public static BinaryContent Create(BinaryData value); needs to copy the MediaType from BinaryData to BinaryContent.

BinaryData doesn't have a MediaType property - it's a basic byte container from the .NET BCL. Could you clarify how to get the MediaType from BinaryData? Should the Create(BinaryData) method continue to return null for MediaType as it currently does, or is there another mechanism to determine the content type?

[KrzysztofCwalina]

The CI fails because the new PAIs are not AOT compliant:
Found 2 additional warnings that were not expected:
//sdk/core/System.ClientModel/src/Message/BinaryContent.cs(91): Trim analysis warning IL2026: System.ClientModel.BinaryContent.CreateJson(T,JsonSerializerOptions): Using member 'System.BinaryData.FromObjectAsJson(T,JsonSerializerOptions)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. JSON serialization and deserialization might require types that cannot be statically analyzed. [D:\a_work\1\s\eng\scripts\compatibility\TempAotCompatFiles\aotcompatibility.csproj]
//sdk/core/System.ClientModel/src/Message/BinaryContent.cs(91): AOT analysis warning IL3050: System.ClientModel.BinaryContent.CreateJson(T,JsonSerializerOptions): Using member 'System.BinaryData.FromObjectAsJson(T,JsonSerializerOptions)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. JSON serialization and deserialization might require types that cannot be statically analyzed and might need runtime code generation. [D:\a_work\1\s\eng\scripts\compatibility\TempAotCompatFiles\aotcompatibility.csproj]
Deleting test app files.

I think you need to apply AOT annotations and/or support context. See how BinaryData does it at
https://github.com/dotnet/runtime/blob/main/src/libraries/System.Memory.Data/src/System/BinaryData.cs#L88

[Copilot]

The CI fails because the new PAIs are not AOT compliant:
Found 2 additional warnings that were not expected:
/_/sdk/core/System.ClientModel/src/Message/BinaryContent.cs(91): Trim analysis warning IL...

Added AOT compliance attributes (RequiresDynamicCode and RequiresUnreferencedCode) to the CreateJson(T, JsonSerializerOptions?) method to resolve the IL2026 and IL3050 warnings. The attributes follow the same pattern used by BinaryData.FromObjectAsJson. Updated API surface files accordingly. Commit b34f3f1

[KrzysztofCwalina]

/check-enforcer override