Merge branch 'jh/builtin-fsmonitor' into seen

Merge branch 'jh/builtin-fsmonitor' into seen

An attempt to write and ship with a watchman equivalent tailored
for our use.

What's the status of this one?

* jh/builtin-fsmonitor: (28 commits)
  t/perf: avoid copying builtin fsmonitor files into test repo
  t7527: test status with untracked-cache and fsmonitor--daemon
  p7519: add fsmonitor--daemon
  t7527: create test for fsmonitor--daemon
  fsmonitor: force update index after large responses
  fsmonitor: enhance existing comments
  fsmonitor--daemon: use a cookie file to sync with file system
  fsmonitor--daemon: periodically truncate list of modified files
  fsmonitor--daemon: implement handle_client callback
  fsmonitor-fs-listen-macos: implement FSEvent listener on MacOS
  fsmonitor-fs-listen-macos: add macos header files for FSEvent
  fsmonitor-fs-listen-win32: implement FSMonitor backend on Windows
  fsmonitor--daemon: create token-based changed path cache
  fsmonitor--daemon: define token-ids
  fsmonitor--daemon: add pathname classification
  fsmonitor--daemon: implement daemon command options
  fsmonitor-fs-listen-macos: stub in backend for MacOS
  fsmonitor-fs-listen-win32: stub in backend for Windows
  t/helper/fsmonitor-client: create IPC client to talk to FSMonitor Daemon
  fsmonitor--daemon: implement client command options
  ...