How to import from indirect dependency to package extension

[gdalle]

In my package DifferentiationInterface.jl, the Zygote extension also depends explicitly on ForwardDiff, even though ForwardDiff is a dependency of Zygote too:

JuliaDiff/DifferentiationInterface.jl/blob/cc8818a2bb0fb3dab2abf29ba213f89213a8613a/DifferentiationInterface/Project.toml#L44

This allows me to do import ForwardDiff in the extension instead of import Zygote.ForwardDiff