assistant2: Use icons for tool call status communication (#26617)

It was hard to catch the running & pending states, though. When running,
it will appear as a spinning arrow circle icon.

<img
src="https://github.com/user-attachments/assets/dbf1bc0a-6fa3-41c6-bcd7-2226e89c87b4"
width="500px" />

Release Notes:

- N/A