Convert category__and query into category__in when only one category passed in

[batmoo]

If a category__and query gets only one term passed in, it still builds out the complex query required for the AND lookup, which can be pretty expensive (#16706).

We should be smarter and automatically convert the query into a category__in when category__and only gets passed in one category.

[wonderboymusic]

Mo, take a look and see if this patch accomplishes what you want, I think it does

[wonderboymusic]

In 25238:

Convert category__and to category__in (less expensive) and unset it when only one category is passed. Adds unit tests.

Fixes #24245.