Synchronously flushes any pending data and metadata operations of the given file stream to disk.

const file = Deno.openSync(
  "my_file.txt",
  { read: true, write: true, create: true },
);
file.writeSync(new TextEncoder().encode("Hello World"));
file.truncateSync(1);
Deno.fsyncSync(file.rid);
console.log(Deno.readTextFileSync("my_file.txt")); // H