ZZ.random_element gives incorrect description of mpz_rrandomb distribution

[paiv]

The reference for ZZ.random_element gives this description:

If the distribution 'mpz_rrandomb' is specified, the output is in the range from 0 to 2^x-1.

This does not match the GMP description:

The random number will be in the range 2^n-1 to 2ⁿ-1, inclusive.

And can be observed with

sage: histogram([ZZ.random_element(1, distribution='mpz_rrandomb') for _ in range(100)])

The reference manual should be updated to reflect actual behavior of mpz_rrandomb.

If we want the originally described range 0 to 2^x-1, mpz_urandomb should be added as a supported distribution.

Depends on #12496

Component: documentation

Issue created by migration from https://trac.sagemath.org/ticket/32319