ngl: Use fp16 for colors
This reduces the size of our Vertex struct from 48 to 24 bytes.
As for, why this is using fp16 instead of rgba8888:
- we already have colors as floats, and do some cpu-side computations on them, so going back to rgba8888 might incur rounding errors
- some vague thoughts about hdr content (might be irrelevant, since such content would probably be in textures)
Edited by Matthias Clasen