rand: implement an unbiased random integer from a range

rand: implement an unbiased random integer from a range

Refer: https://github.com/apple/swift/pull/39143 for a description
of the algorithm.

It is optimal in the sense of having:

* no divisions
* minimal number of blocks of random bits from the generator

Reviewed-by: Tom Cosgrove <tom.cosgrove@arm.com>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22499)