Update RectBlur FP to use main(float2).
Update RectBlur FP to use main(float2).

Change-Id: Ifc8689f4f7cb323070341572443e1a2d14a4aed4
Bug: skia:13737
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/580961
Commit-Queue: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Commit-Queue: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>
Reviewed-by: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia,google/skia