MAINT: remove outdated xp_ functions, xp.asarray on elementwise function args

[mdhaber]

Reference issue

gh-22680

What does this implement/fix?

Now that the 2024.12 standard is out and array-api-compat supports it, I thought it was time for a cleanup of some artifacts from the old days of array API translations.

One of the things we used to have to do was convert arguments to xp.where, xp.minimum, etc., into arrays rather than leaving them as scalars. Even if we were careful to use the correct dtype, I don't think anyone ensured that the array ended up on the correct device. Use of a Python scalar avoids both of these gotchas.

This cleans up most of the now-unnecessary array conversions in the context of xp.where, xp.minimum, xp.clip, and some other elementwise functions mentioned in data-apis/array-api#807 (comment). I also noticed some old custom xp_ functions that we no longer need since they are provided by array-api-compat.

Lots of lines and files are changed, but it should be pretty straightforward.

Additional information

Based on gh-22680, I think that anywhere we create an array within a function, we need to pay attention to the device. This only avoids some of those places. To resolve that issue, we really should test with non-default devices (and make the required changes).

There may be some test skips we can remove now. I think we can do that as part of follow-up to gh-22609/gh-22677.

Use of result_type needs very special attention; see data-apis/array-api-compat#223 (comment). Now that it's possible, we need to make sure we pass the arguments to result_type before they become arrays.

[mdhaber]

Failures are due to data-apis/array-api-compat#271 and data-apis/array-api-strict#131.

[j-bowhay]

Thanks for the tidy up!