Read Reader r until EOF (null) and resolve to the content as Uint8Array`.

  // Example from stdin
  const stdinContent = await Deno.readAll(Deno.stdin);

  // Example from file
  const file = await Deno.open("my_file.txt", {read: true});
  const myFileContent = await Deno.readAll(file);
  Deno.close(file.rid);

  // Example from buffer
  const myData = new Uint8Array(100);
  // ... fill myData array with data
  const reader = new Deno.Buffer(myData.buffer as ArrayBuffer);
  const bufferContent = await Deno.readAll(reader);