Create rand function for Base.KeySet and Base.ValueIterator{Dict}

[Tortar]

Fixes #51605 .

I also created a version of rand for Base.ValueIterator{Dict} which currently throws an error.

[oscardssmith]

Does this work as is or do you also need to define the Sampler constructor? (not rhetorical, I actually don't know the answer)

[Tortar]

Tested with Revise before doing the PR to see if benchmark results improved and they did, it should work as it is.

Also I think the constructor is already defined and called here:

julia/stdlib/Random/src/Random.jl

Line 253 in 419af92

rand(rng::AbstractRNG, X) = rand(rng, Sampler(rng, X, Val(1)))

[rfourquet]

LGTM, but this would need tests which exercise the new code paths.

[Tortar]

tests added and locally run 👍