Use a virtualized FlowLayoutPanel for the rcheevos achievments form

[Morilli]

See #4479. Currently WIP and kinda garbage code, not yet sure how to structure this. But it should generally work.

todo:

• [x] handle form resizing
• [ ] make this implementation less manual and hacky

Check if completed:

• [ ] I have run any relevant test suites
• [x] I, the commit author, have read the licensing terms for contributors (last updated 2024-06-22) and am compliant

[Morilli]

By the way this is about ready from my side. I'm still not too happy with the code structure but it works and fixes the issue, so 🤷.

Unless there's complaints I'd like to merge this soon so we have a working achievements and leaderboards form for the next release.

Edit: Seems to crash in my wsl ubuntu because OnSizeChanged is called during InitializeComponent... sigh