[skottie] Simplify layer matrix caching

Switch to SkTHashMap, unify the cache based on layer index.

TBR=

Change-Id: I7e7622571156d67b4fe5ef91ee9a9a49b089c78f
Reviewed-on: https://skia-review.googlesource.com/101001
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
1 file changed