[skottie] Split-up Skottie.cpp

Introduce more granular compilation units for major Skottie layer types.

TBR=
Change-Id: Iee2ef05cbcdda06467674824eb295ae6d7dc5bb9
Reviewed-on: https://skia-review.googlesource.com/148394
Commit-Queue: Florin Malita <fmalita@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
7 files changed