[skottie] Add build rule for final Skottie image

Add a build rule to layer CanvasKit on top of the base
Skottie to produce the final Skottie Docker image.

Bug: b/296813475
Change-Id: I38bf040548f989b32e31f3b7b88a3b68236ff640
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/745456
Reviewed-by: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Chris Mumford <cmumford@google.com>
6 files changed