Escape ampersand char for Windows

[archiif]

Ampersand characters in subtitles causes issues because it is a reserved character in cmd, so we need to escape them.
https://stackoverflow.com/a/35578027/10625876

[archiif]

Actually, I just realized that this is the tip of the iceberg of what is a pretty serious injection vulnerability.
Maybe a more robust solution is needed?
mpv-player/mpv#4695 (comment)
If you use the external program copyq like this, without spawning cmd:

mp.commandv("run", "copyq", "copy", text)

It no longer trips up on any special characters. But it adds a dependency, so I'm open to better solutions.

[tatsumoto-ren]

Using powershell instead of cmd on Windows to copy text to clipboard would be a possible workaround.

[archiif]

I personally find powershell to be undesirably slow, but that might be due to my old PC.
You also could use the stdin_data argument in mpv's subprocess command so that you can pipe the subtitle string to clip safely, but for some reason that argument doesn't work, at least on Windows.
I opened an issue about it here:
mpv-player/mpv#8503

[tatsumoto-ren]

Yes, I always tell people to switch to GNU/Linux because Windows is a nightmare. If you're new to GNU/Linux, I recommend Manjaro, it's easy to install and comes with one of the fastest package managers out there - Pacman.

I'm going to merge the pull request because any solution is better than no solution. If a better way to handle this bug is found, we can just revert the commit later.