Synchronously read from the file into an array buffer (p).

Returns either the number of bytes read during the operation or EOF (null) if there was nothing more to read.

It is possible for a read to successfully return with 0 bytes. This does not indicate EOF.

It is not guaranteed that the full buffer will be read in a single call.

// if "/foo/bar.txt" contains the text "hello world":
using file = Deno.openSync("/foo/bar.txt");
const buf = new Uint8Array(100);
const numberOfBytesRead = file.readSync(buf); // 11 bytes
const text = new TextDecoder().decode(buf);  // "hello world"