Add ScopedValues to export list for Base

[CameronBieganek]

This will allow users to type ScopedValues.with without having to do a using or import. (As can be done for Iterators.take and Threads.nthreads, etc.)

This needs to be backported to 1.11, in my opinion.

[nsajko]

Why clutter the main namespace? I think Base.ScopedValues is fine.

[LilithHafner]

This could be confusing if someone loads the ScopedValues.jl package (e.g. for compat with Julia < 1.11)

[CameronBieganek]

Why clutter the main namespace? I think Base.ScopedValues is fine.

Do you think Base.ScopedValues.ScopedValue(x) is fine? Or Base.ScopedValues.with? I think exporting ScopedValues makes sense given that we do the same thing for commonly used modules like Iterators, Threads, and Sys. "Why clutter the namespace?" is an argument that I'm getting tired of hearing. It lacks substance. Why not make ScopedValues convenient and ergonomic to use?

But yeah, the situation with ScopedValues.jl is unfortunate.