Flushes any pending data operations of the given file stream to disk.

const file = await Deno.open("my_file.txt", { read: true, write: true, create: true });
await Deno.write(file.rid, new TextEncoder().encode("Hello World"));
await Deno.fdatasync(file.rid);
console.log(new TextDecoder().decode(await Deno.readFile("my_file.txt"))); // Hello World