The strategy for how individual files are watched.

• fixedPollingInterval: Check every file for changes several times a second at a fixed interval.
• priorityPollingInterval: Check every file for changes several times a second, but use heuristics to check certain types of files less frequently than others.
• dynamicPriorityPolling: Use a dynamic queue where less-frequently modified files will be checked less often.
• useFsEvents (the default): Attempt to use the operating system/file system's native events for file changes.
• useFsEventsOnParentDirectory: Attempt to use the operating system/file system's native events to listen for changes on a file's parent directory