Lots of duplicated content from concepts, missing pointers to the second
half of the tool calling loop
Simpler + more focused + a more prominent link to the second half of the
loop was what I was aiming for, but down to be more conservative and
just more prominently link the "passing tools back to the model" guide.
I have also moved the tool calling conceptual guide out from under
`Structured Output` (while leaving a small section for structured
output-specific information) and added more content. The existing
`#functiontool-calling` link will go to this new section.
