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:

• handle form resizing
• make this implementation less manual and hacky

Check if completed:

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