[libc][math][c23] adds `nanf128` (#85201)

Continuing #84689, this one required more changes than the others, so I
am making it a separate PR.

Extends some stuff in `str_to_float.h`, `str_to_integer.h` to work on
types wider than `unsigned long long` and `uint64_t`.

cc @lntue for review.

GitOrigin-RevId: b43965adacfafc4dc6b5ec17b4bea839372b7626
15 files changed