export jl_alloc_array_nd, re-add convenience wrappers

[benlorenz]

This is used in an example here in the docs https://docs.julialang.org/en/v1.11-dev/manual/embedding/#Multidimensional-Arrays and needed to adapt to the removed jl_alloc_array_2d (#51319).

I also added inline convenience wrappers for jl_alloc_array_2d and jl_alloc_array_3d to un-break existing code, both functions were removed in the Memory PR in favor of the _nd variant. If this is undesired I can remove them again and only keep the new export.

[Taaitaaiger]

Could you also export the 2d and 3d constructors instead of marking them as static inline? I use both those functions in jlrs and dealing with static inlines is kind of awkward.

[benlorenz]

Could you also export the 2d and 3d constructors instead of marking them as static inline? I use both those functions in jlrs and dealing with static inlines is kind of awkward.

I think that's reasonable since they were exported before, done in 4e6e1a7.

[Taaitaaiger]

Thanks, I appreciate it!

[fingolfin]

It would be great to have this, to unbreak some JLLs resp. allow us to fix them w/o too much of a headache.