Move `rand_pcg` to the rngs repository?

[newpavlov]

After rand_core migration to its own repository and chacha20 replacing rand_chacha, rand_pcg will be the only remaining "additional" crate in this repository. I think it makes sense to move it to the rust-random/rngs repository and use this repository only for the rand crate.

[dhardy]

rand_pcg is used by the benches crate, hence why it is the only PRNG crate here.

It may be fine to port the benches to use Xoshiro (as implemented in rand).

[newpavlov]

rand_pcg is used by the benches crate,

Why can't we use rand_pcg from crates.io or using rand_pcg = { git = "..." } (for pre-release versions)?

[dhardy]

Because I don't want to make things more complicated without good reason.

[newpavlov]

I don't see a big complexity difference between rand_pcg = { path = "../rand_pcg" } and rand_pcg = "0.10". It would require some maintenance action during release of a new breaking rand_core release, but considering that it should be an extremely rare event, it's arguably not a big issue. Especially considering that we would have to update the benches from rand_chacha to chacha20.

Migrating the benches to Xoshiro and StdRng is fine as well.

[dhardy]

rand_pcg was here for the same reason I was reluctant to depend on chacha20 as an out-of-dependency tree, but since we already moved rand_core to a new repo there's no longer a good reason to worry about moving rand_pcg.