Reduce type piracy by shifting methods to AbstractFFTs

[jishnub]

GenericFFT.jl/src/GenericFFT.jl

Lines 24 to 33 in 2e55016

	AbstractFFTs.complexfloat(x::StridedArray{Complex{<:AbstractFloat}}) = x
	AbstractFFTs.realfloat(x::StridedArray{<:Real}) = x
	# We override this one in order to avoid throwing an error that the type is
	# unsupported (as defined in AbstractFFTs)
	AbstractFFTs._fftfloat(::Type{T}) where {T <: AbstractFloat} = T
	# We also avoid any conversion of types that are already AbstractFloat
	# (since AbstractFFTs calls float(x) by default, which might change types)
	AbstractFFTs.fftfloat(x::AbstractFloat) = x
	# for compatibility with AbstractFFTs
	AbstractFFTs.fftfloat(x::Float16) = Float32(x)

These should ideally be moved to AbstractFFTs to reduce the type-piracy in this package.

[daanhb]

Yes, that would be more appropriate. Although it may have side-effects, but even then it would be worth fleshing them out.