In order to reduce our reliance on __builtin_{ffs, clz, ctz, popcount},
this commit removes all calls to these functions and replaces them with
the equivalent functions in AK/BuiltinWrappers.h.
This algorithm allows for much faster computations of modular powers
(around a 5x-10x speedup of the Crypto test). However, it is only valid
for odd modulo values, and therefore the old algorithm must be kept for
computations involving even modulo values.
Since the operations are already complicated and will become even more
so soon, let's split them into their own files. We can also integrate
the NumberTheory operations that would better fit there into this class
as well.
This commit doesn't change behaviors, but moves the allocation of some
variables into caller classes.
