Move searchsorted* functions to SortedSearch stdlib module

[nalimilan]

Keep them under Base.Sorted but unexported, since they are used in a few places in Base, in particular for sparse vectors and matrices.

Fixes #24883.

[KristofferC]

In my opinion this feels way to specific to be a stdlib module.

[nalimilan]

Yeah, it's not a lot of functionality for a single module. So would you recommend moving them to a package (new or existing) instead?

[JeffBezanson]

Why do you hate these functions so much? :)
I think we should leave them alone.

[nalimilan]

It's just that they don't follow the naming pattern used for all find* functions, so they look really out of place (after #24673). Why use the term "search" when the API consistently uses "find" in other areas?

There's also the possibility of merging them with standard find* functions using a Sorted wrapper, whose interest hasn't been discussed yet.

[KristofferC]

If it is "just that they don't follow the naming pattern" can't they just be renamed then?

As to a sorted wrapper, if it is only used for dispatch, it seems to not solve any concrete problem but add additional ones.

[nalimilan]

Yes, renaming them as another option. (Note that I had initially made this PR in the perspective of merging all breaking changes around December 15th, considering that it was simpler to move things to sdlib when we didn't have time to discuss these issues in depth. But since we took that design discussion time, it may not be the most appropriate action now.)

[nalimilan]

I've opened #25414 implementing the less radical approach of renaming these functions.