[canvaskit] Consolidate Skottie assets

 - use a single name -> SkData map for both images and fonts

 - consolidate images/fonts as a generic "assets" API

 - pass pre-constructed asset maps to the SkottieAssetManager factory
   and remove setter (immutable class at this point)

Bug: skia:
Change-Id: Ief6d3bcbba339ccd1d81fd9950871eaa691ee947
Reviewed-on: https://skia-review.googlesource.com/c/196503
Reviewed-by: Kevin Lubick <kjlubick@google.com>
3 files changed