Merge branch 'jh/fsmonitor-prework'

Merge branch 'jh/fsmonitor-prework'

Preliminary changes to fsmonitor integration.

* jh/fsmonitor-prework:
  fsmonitor: refactor initialization of fsmonitor_last_update token
  fsmonitor: allow all entries for a folder to be invalidated
  fsmonitor: log FSMN token when reading and writing the index
  fsmonitor: log invocation of FSMonitor hook to trace2
  read-cache: log the number of scanned files to trace2
  read-cache: log the number of lstat calls to trace2
  preload-index: log the number of lstat calls to trace2
  p7519: add trace logging during perf test
  p7519: move watchman cleanup earlier in the test
  p7519: fix watchman watch-list test on Windows
  p7519: do not rely on "xargs -d" in test