* Create "extension guides" section
* Sort developer notes into subsections
* Move examples from advanced section into user guides
* Reorder some listings, adjust some titles
Building on #21925, this tutorial demonstrates the use of the FFI using
`ffi_call` with a simple example. I don't think this should cover all of
the most advanced use cases, but it should be sufficient for the most
common examples. I think it would be useful to eventually replace the
existing CUDA tutorial, but I'm not sure that it'll get there in the
first draft.
As an added benefit, this also runs a simple test (akin to
`docs/cuda_custom_call`) which actually executes using a tool chain that
open source users would use in practice.
