replace masking rasterizer with a more simple geometry based rasterizer (for the compositor).

notes:
- uncomment  #define USE_RASKTER in BKE_mask.h to use the previous mask rasterizer.
- slightly slower for regular masks but significantly faster for feather.
- main benefit is that it threads well so works nice for tile compositor.
- feather is lower quality, can use some improvements here.
- feather can also use some interpolation enhancements, will do later.

source/blender/blenkernel/BKE_mask.h

@@ -206,7 +206,7 @@ void BKE_mask_init_layers(Mask *mask, struct layer_init_data *mlayer_data, int w
 #define MASKPOINT_DESEL_HANDLE(p)   { (p)->bezt.f1 &= ~SELECT; (p)->bezt.f3 &= ~SELECT; } (void)0
 
 /* disable to test alternate rasterizer */
-#define USE_RASKTER
+/* #define USE_RASKTER */
 
 /* mask_rasterize.c */
 #ifndef USE_RASKTER