Force positions to scale by 128/32768 as the psp does

Haven't measured the performance impact carefully on mobile, but I'm hoping it's small.

Fixes #1963, fixes #4617, fixes #2077, and reportedly fixes glitches in other games too.

Note that normals were and still are converted using varying methods currently: software uses 127/32767, hardware may use 127.5/32767.5 or 128/32768 depending on skin/morph.  However, position should with these changes be the same everywhere.

Does not round positions correctly, which may or may not be important, but this gets us closer to accurate anyway in a way that definitely fixes some issues.

-[Unknown]