fs: improve `cpSync` performance

[anonrig]

By moving the function to C++, we should get a significant improvement in performance.

I'm extremely open to suggestions on improving the benchmarks, but with the current state, here are the results:

local benchmarks

macOS M1 Max

                           confidence improvement accuracy (*)    (**)   (***)
fs/bench-cpSync.js n=1            ***     63.75 %      ±10.38% ±13.83% ±18.03%
fs/bench-cpSync.js n=100          ***    607.18 %      ±46.07% ±62.03% ±82.22%
fs/bench-cpSync.js n=10000        ***    690.84 %      ±30.74% ±41.37% ±54.83%

Be aware that when doing many comparisons the risk of a false-positive result increases.
In this case, there are 3 comparisons, you can thus expect the following amount of false-positive results:
  0.15 false positives, when considering a   5% risk acceptance (*, **, ***),
  0.03 false positives, when considering a   1% risk acceptance (**, ***),
  0.00 false positives, when considering a 0.1% risk acceptance (***)

benchmark ci

19:04:42                            confidence improvement accuracy (*)    (**)   (***)
19:04:42 fs/bench-cpSync.js n=1            ***    154.37 %       ±6.67%  ±8.88% ±11.57%
19:04:42 fs/bench-cpSync.js n=100          ***    163.66 %       ±9.09% ±12.22% ±16.16%
19:04:42 fs/bench-cpSync.js n=10000        ***    103.21 %       ±0.96%  ±1.28%  ±1.67%

benchmark ci: https://ci.nodejs.org/view/Node.js%20benchmark/job/benchmark-node-micro-benchmarks/1572/