Synchronously flushes any pending data 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"));
Deno.fdatasyncSync(file.rid);
console.log(Deno.readTextFileSync("my_file.txt")); // Hello World