fsmonitor: fsmonitor should send wlock notifications to watchman The fsmonitor extension should send state-enter and state-leave notifications to watchman when the wlock is acquired/release, respectively. This will allow watchman and watchman subscribers to customize behavior based on whether source control operations are occurring. Test Plan: Tested checkout, update and working copy changes with extension enabled. Differential Revision: https://phab.mercurial-scm.org/D1612