RFR: 8293067: (fs) Implement WatchService using system library (macOS) [v9]

[Michael Hall]

> On Nov 10, 2022, at 5:36 AM, Maxim Kartashev <maxim.kartashev at jetbrains.com> wrote:
> 
> I benchmarked this implementation (well, the implementation this one is based on, now it's become quite different) extensively. The main advantage of FSEvents over polling was near-0 CPU usage when there were small number of changes to the directory being watched, while polling naturally always has some background job to do and its CPU usage heavily depends on refresh speed (like 25% with SENSITIVITY_HIGH and modest rate of changes).
> 

For this FSEvents did show near 0 cpu. Polling showed some but was still very low. It didn’t appear significant.
Again, other benchmarking that stressed different things might reveal other results.