Random: Mark unexported public symbols as public (#55148)

The following symbols:
`seed!, default_rng, Sampler, SamplerType, SamplerTrivial,
SamplerSimple` Are documented in the Julia documentation and unexported,
but not marked as public.

Co-authored-by: Max Horn <[email protected]>

Author: jakobnissen

stdlib/Random/src/Random.jl

@@ -29,6 +29,8 @@ export rand!, randn!,
        randcycle, randcycle!,
        AbstractRNG, MersenneTwister, RandomDevice, TaskLocalRNG, Xoshiro
 
+public seed!, default_rng, Sampler, SamplerType, SamplerTrivial, SamplerSimple
+
 ## general definitions
 
 """