Converting scale array in adjoint plan application fails for subarrays

[gaurav-arya]

The code convert(typeof(x), scale) fails when x is a subarray, e.g. in line

AbstractFFTs.jl/src/definitions.jl

Line 641 in 1cc9ca0

return p.p \ (x ./ convert(typeof(x), scale))

It would also fail if x is e.g. a Zygote.OneElement, e.g. in the context of the plan reverse rule.

---

Jax's implementation for reference: https://github.com/google/jax/blob/c3aa3a4c312826cdfb0d617e30f0467c18ab4564/jax/_src/lax/fft.py#L211. Not terribly useful here because there they have no problems with generic broadcasting array construction

[gaurav-arya]

It also fails when x is a Zygote.OneElement, causing test failures in Zygote: see https://github.com/FluxML/Zygote.jl/actions/runs/5787572971/job/15684783986 and discussion in FluxML/Zygote.jl#1444.