random: Split the uint128 implementation into its own header (#13132)

The implementation of `php_random_uint128_*` exists specifically for
pcgoneseq128xslrr66 and takes up a third of php

random: Split the uint128 implementation into its own header (#13132)

The implementation of `php_random_uint128_*` exists specifically for
pcgoneseq128xslrr66 and takes up a third of php_random.h. Split it into its own
header to keep php_random.h focused on the functionality directly related to
randomness.

show more ...