Fixed + Updated app using Microsoft Copilot V2

I... fixed the app and adapted it to Microsoft Copilot V2...

Here's my fork: foxypiratecove37350/BingChat.

Here's a non-exhaustive list of what I did (because there are probably things that I did then forgot about):

• Additions
  • Add a warning before reloading the page
• Fixes
  • Fix the new topic feature
• Changes
  • Use new Microsoft Copilot URL
  • Change the way to switch themes, now no need of restarting the program anymore
  • Update the Markdown export output
  • Support now Ctrl + Numpad Plus/Minus shortcuts for changing the font size
  • Use now scale factors for font size
• Removals
  • Remove "Switch tone", "Quick reply" and "Stop responding" shortcuts as they're not features of Microsoft Copilot anymore

I aim to maintain my fork, but I'm not sure if there are other things to really do. Probably some bug fixes and some minor feature additions.