Fix point in polygon

[pushfoo]

• Fix get_sprites_at_point broken #2253 by hardcoding a horizontal edge case (Ty @FengchiW !)
• Split up some tests
• Partial smoke test tool for collisions

Unless there's a good reason to wait, I suggest merging this once remaining test issues get straightened out.

[einarf]

Remaining work:

• Sanity check fix
• Ensure the new geometry tests at least covers the basics¨
• Look into broken sprite tests