Support f!(y, x) for Zygote with Zygote.Buffer

[gdalle]

See https://fluxml.ai/Zygote.jl/stable/utils/#Zygote.Buffer

Ping @Vaibhavdixit02

[gdalle]

PR #360 fails because

Buffer is not an AbstractArray and can't be used for linear algebra operations like matrix multiplication. This prevents it from being captured by pullbacks.

and some functions are typed f!(y::AbstractArray, x::AbstractArray). I think in general this fix would only cover a very limited subset of possible mutating operations, so I'm not sure it's worth it

[Vaibhavdixit02]

Wait, I think the main thing it does, and what I had in mind asking for it was supporting in-place functions that's it. It has been quite robust in my experience and by documenting that the extent of mutation here is just in-place function calls why is this not worth it? Doesn't that mean that you'd be able to mark off the Two-argument column for Zygote here https://gdalle.github.io/DifferentiationInterface.jl/DifferentiationInterface/dev/backends/#Features?

[gdalle]

Gonna give it another try. Hopefully all it takes is to remove a few type annotations for my test suite to pass

[gdalle]

Buffer was discussed on Slack today and described as very hacky and buggy, so I think this feature would cause more harm than good in the end.