Synchronously reads Reader r until EOF (null) and returns the content as Uint8Array.

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

  // Example from file
  const file = Deno.openSync("my_file.txt", {read: true});
  const myFileContent = Deno.readAllSync(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 = Deno.readAllSync(reader);