fix bug: AiMessage text content is not copied when toolCalls are pres…

[hrhrng]

Issue

#986

Change

When OpenAI returns both content and tool_calls, keep them all instead of just keeping the tool_calls.

General checklist

• There are no breaking changes
• I have added unit and integration tests for my change
• I have manually run all the unit and integration tests in the module I have added/changed, and they are all green
• I have manually run all the unit and integration tests in the core and main modules, and they are all green
• I have added/updated the [documentation

[langchain4j]

HI @hrhrng, thank you! I wil ltry to review it asap