Make color-related ops take the ccs and a GdkColor, and make
decisions about color conversion on the cpu vs the gpu.
This makes the node processor code simpler, and lets use convert
the color directly into the op instance without extra copying.
We also pass opacity to the op, so it can be applied when we
write the color into the instance.
Lastly, rorder the offset to come right after the opacity argument.
Treat the color and rounded color ops the same way.
Update all callers.
With this, the prepare_color apis in gskgpunodeprocessor.c are
no longer used and have been dropped.
There's multiple uses I want it for:
1. Generating the box-shadow area for blurring
2. Generating masks for rounded-rect masking
3. Optimizing the common use case of rounded-clip + color
Only the last one is implemented in this commit.
