code: static Set<String> getSubmounts(VirtualFile virtualFile) {
          final ConcurrentMap<VirtualFile, Map<String, Mount>> mounts = VFS.mounts;
          final Map<String, Mount> mountMap = mounts.get(virtualFile);
          if (mountMap == null) {
              return emptyRemovableSet();
          }
          return new HashSet<String>(mountMap.keySet());
      }
docs: Get all immediate submounts for a path.
  
  @param virtualFile the path
  @return the collection of present mount (simple) names