Support recording replays in web

[lukexor]

Desktop supports recording game replays to the users data directory based on OS without user interaction. In web, downloading files requires the user to interact.

This could be done by showing a message with a 'Download' button when the recording is stopped, allowing the user to download it or discard it.

Some reference JS code for how this might work (will need to be converted to Rust):

const blob = new Blob([binEncodedData], {
  type: "application/octet-stream",
});

const url = URL.createObjectURL(blob);
const a = document.createElement("a");
a.href = url;

a.download = "demo.replay";
document.body.appendChild(a);
a.click();

document.body.removeChild(a);
URL.revokeObjectURL(url);