Add support for scalar arguments to xp.where

[betatim]

This is related to data-apis/array-api#807

This only adds support for scalars to where(). If the second or third argument is a scalar it is turned into an array on the same device as condition.

I added 2024.12 as next_supported_version. This means we can use it in the tests. Not sure if we use some kind of dummy value instead of 2024.12?

[asmeurer]

Some of this overlaps with the stuff I've done over at #82, although I haven't implemented any scalar stuff there yet because it isn't in the standard yet.

[ev-br]

I'd think it should allow complex x1 and x2, too. Here and in the annotation.

LGTM otherwise!

[ev-br]

There's a conflict now, could you please resolve it?

Also, the spec requires that at least one of x1 and x2 is an array. IIUC, this PR allows both of them to be python scalars. As long as this repo is scrupulous in implementing the spec, it should probably check and error out if both are scalars?

[ev-br]

A small update to make it adhere to the spec to the letter: betatim#1

[betatim]

Thanks for the PR @ev-br If you'd like to take over the original PR (this PR) to get it done that would be awesome.

[ev-br]

Happy to oblige @betatim --- thank you!