Flushes any pending data and metadata 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.ftruncate(file.rid, 1);
await Deno.fsync(file.rid);
console.log(new TextDecoder().decode(await Deno.readFile("my_file.txt"))); // H