build(webpack): reduce production source maps

[ShGKme]

☑️ Resolves

Reduce /js directory size on production from 170 MB to 90 MB

• Application size in the /apps/spreed folder is about 210 MB, with 170 MB (80%) js/ folder
• It includes .map files with 120 MB (70% of js/, 57% of /apps/spreed)
• Getting rid of SourceMaps completely would make bug reporting much more complicated
• However, we can use less expensive source maps with only original file names and lines, but not entire source content
• This makes .map 3 times smaller, or /apps/spreed 60% smaller

Stuff	🏚️ Before	🏡 After
App folder	210 MB 🟦🟦🟦🟦🟦	130 MB 🟦🟦🟦
JS folder	170 MB 🟦🟦🟦🟦	90 MB 🟦🟦🟦
.js.map	120 MB 🟦🟦🟦	40 MB 🟦

🏁 Checklist

• 🌏 Tested with different browsers / clients:
  • Chromium (Chrome / Edge / Opera / Brave)
  • Firefox
  • Safari
  • Talk Desktop
  • Not risky to browser differences / client
• 🖌️ Design was reviewed, approved or inspired by the design team
• ⛑️ Tests are included or not possible
• 📗 User documentation in https://github.com/nextcloud/documentation/tree/master/user_manual/talk has been updated or is not required

[DorraJaouad]

[Antreesy]

Fixable with $csp->addAllowedScriptDomain("'unsafe-eval'"); adding to CSPListener.php. Need to check if this is fine to modify it for all cases, or only with xdebug flag

But I'm not sure about prod sourcemaps, is this expected?

[ShGKme]

We can also use cheap-source-map for development wich has the same source maps quality but slower rebuild in watch mode.

[ShGKme]

Done, but I'll wait for Joas before mergin

[ShGKme]

@nickvergessen What do you think?