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