Propagate etag changes when the watcher finds a changed file

Depends on #11409 

Currently when a file is changed directly on an external filesystem and the change is detected, the etag isn't properly propagated to the root.

cc @PVince81 @DeepDiver1975 
So if I understand well: as soon as the file scanner finds a change in the remote filesystem, it will register it to the propagator which will in turn update the etag of all parent directories, is that correct ?