Improve the situation with the stimes cycle

Currently the Semigroup stimes cycle is resolved in GHC.Base by
importing stimes implementations from a hs-boot file. Resolve the cycle
using hs-boot files for required classes (Num, Integral) instead. Now
stimes can be defined directly in GHC.Base, making inlining and
specialization possible.

This leads to some new boot files for `GHC.Num` and `GHC.Real`, the
methods for those are only used to implement `stimes` so it doesn't
appear that these boot files will introduce any new performance traps.

Metric Decrease:
    T13386
    T8095
Metric Increase:
    T13253
    T13386
    T18698a
    T18698b
    T19695
    T8095