Convert `1:ndims(X)` to `ntuple(identity, ndims(X))`

An example:
https://github.com/JuliaMath/AbstractFFTs.jl/blob/a25656dfabf0f6c5067bc3f90a591c242da4b9be/src/definitions.jl#L62

Using a `Tuple` here will allow `ndims` to be constant-propagated without relying on the compiler. It also reduces allocations in various functions, as vectors don't need to be allocated.
Such a change would be mildly breaking, but seems worthwhile. FFTW has largely been updated to accept `Tuple`s as regions, and some other dependencies might need to be looked at.