Add data streaming support for tools

[BrianHung]

Feature Description

Add the ability for tools to stream data during their execution. This allows tools to send intermediate data or progress updates while they are running, rather than just returning a final result.

The feature adds:

• Split DataStreamWriter into basic and full interfaces
• Add dataStream parameter to tool execution and onToolCall

Use Cases

Progress updates during long-running tool operations.

Additional context

https://github.com/vercel/ai-chatbot/blob/main/app/(chat)/api/chat/route.ts