add FileContent and ToolOutput

[tinalenguyen]

• backward compatible, does not break existing user code assuming that tool outputs are str
• add more depth to function tool outputs, allowing for ImageContent and FileContent to be passed along with strings, like so:

    @function_tool
    async def get_chart(self, context: RunContext):
        """Returns a chart image and checkup report when the user asks for a chart or visual."""
        with open("mock_checkup_report.pdf", "rb") as f:
            report_data = f.read()
        img_content = ImageContent(image="https://my.clevelandclinic.org/-/scassets/images/org/health/articles/10881-vital-signs")
        file_content = FileContent(name="mock_checkup_report.pdf", data=report_data, mime_type="application/pdf"),
        return "Here is the normal adult vital chart:", img_content, "And the patient report file:", file_content
            

[theomonnom]

Can't this just be?
ToolOutput = ImageContent | FileContent | str

[tinalenguyen]

what if users wanted to pass multiple items from a function tool