Write the contents of the array buffer (p) to the file.

Resolves to 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 = await Deno.open("/foo/bar.txt", { write: true });
const bytesWritten = await file.write(data); // 11