build: migrate nw-builder to v4.19.0

[ayushmanchhabra]

No description provided.

[ayushmanchhabra]

npm run build, npm run test and npm run coverage work. Let me know if there is anything else that needs fixing, that I have missed

[bastimeyer]

Thanks. I'll have a look at the changes in the next couple of days when I get the time.

[bastimeyer]

Sorry for the delay. I have not forgotten about this.

I'll be having a look during the next Streamlink major version bump where some necessary breaking changes will be included which will break the current version of the Twitch GUI. That major version bump will be after the EOL of Python 3.10, which is at the end of the month. The changes I'm talking about affect the hardcoded Streamlink CLI arguments.

The Twitch GUI has also been removed from the homebrew and NixOS packaging repos recently because of the dated NW.js version in use. macOS of course because of x86_64 and NixOS because they deem the old Chromium version insecure, even though we don't run any remote code and only make remote HTTP API calls. The rest is irrelevant anyway. Oh well...