Follow up from the issue in the old repo libretro/flycast#818

After 3 years, I finally was able to build cores myself in order to find the culprit.

Culprit ---> libretro/flycast@a2137ce

libretro/flycast@bc5be5e Last working build.zip

Examples :
Chun-Li's standing pose in CVS 1/PRO at 1280x960 (integer multiple of 640x480, you'll see stripes on non-integer multiple)

Correct Chun-Li :
https://github.com/flyinghead/flycast/assets/47425204/046de5a6-140d-43d7-bd16-d79cc686b4fa

Warped Chun-Li (today's latest core) - Her shoulder is increasing and decreasing :
https://github.com/flyinghead/flycast/assets/47425204/38d775d4-851e-4069-8301-e3c1b2316f44

This only happens on Capcom characters (thus no SNK characters are affected) in CVS because their sprites comes from the CPS2 with a strange ratio, it also happens on all characters from MVC2.

Why is upscaling important for these 2D games ?

1. Sprites from CPS2 have a weird resolution of 384×224 (4/3 non pixel perfect) which doesn't translate well with the Naomi resolution of 640x480 (pixel-perfect 4/3), thus they are horrible at native with pixels from hell
2. MVC2 has 3D stages
3. CVS has 3D elements in the UI