Function spawn_lsp_file_watcher_task 

pub fn spawn_lsp_file_watcher_task(
    supervisor: LspSupervisorHandle,
    logger: LspLogger,
) -> Result<LspFileWatcherHandle, Error>

Spawn the watcher task on the LSP runtime. Returns the handle Editor should keep. Returns Err only if notify itself fails to construct the OS watcher (out of inotify slots, etc.).