Eliminate laser wobbling at large resolutions

[nmlgc]

Diagonal lasers look really bad with geometry scaling. Like everything else in the game, their vertex coordinates are calculated as integer pixels relative to the original 640×480 resolution and SDL can then only scale these integers, not the calculation that originally produced them. As a result, they appear to jump and wobble more and more as the scaled output resolution increases:

Laser.wobble.webm

Technically, the wobbling exists with framebuffer scaling as well, but it sticks out much more when the lasers themselves are rendered at the high-res output resolution.

This wasn't part of the #4 delivery because

1. geometry scaling is only meant to be a fallback option as it's academically inaccurate from a preservation point of view
2. making the SDL port subpixel-accurate to the original D3D output seemed a more important goal to me, which also implied focusing on framebuffer scaling
3. I did not want to start an 11^th push

But I agree that this is a bug that should be fixed if geometry scaling finds its fans.

Requires a slight bit of care to not affect gameplay, since collision detection must continue to use the original fixed-point coordinates. If the fix should remain exclusive to geometry scaling, we wouldn't need a dedicated configuration setting to toggle it because you'd always want to have it on. Otherwise we would, though, as a non-wobbling render would no longer be subpixel-accurate.