[skottie] Use kF16ColorType layers for motion blur

This fixes the result quantization issue.

TBR=
Change-Id: I7b1f6e40792a4032f93aabc96beddaacf6d837c4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/227259
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed