Write data to the given path, by default creating a new file if needed, else overwriting.

  const encoder = new TextEncoder();
  const data = encoder.encode("Hello world\n");
  await Deno.writeFile("hello1.txt", data);  // overwrite "hello1.txt" or create it
  await Deno.writeFile("hello2.txt", data, {create: false});  // only works if "hello2.txt" exists
  await Deno.writeFile("hello3.txt", data, {mode: 0o777});  // set permissions on new file
  await Deno.writeFile("hello4.txt", data, {append: true});  // add data to the end of the file

Requires allow-write permission, and allow-read if options.create is false.