Synchronously write the contents of the array buffer (p) to the file.

Returns the number of bytes written.

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

const encoder = new TextEncoder();
const data = encoder.encode("Hello world");
using file = Deno.openSync("/foo/bar.txt", { write: true });
const bytesWritten = file.writeSync(data); // 11