[skottie] Fix wipe effects for images

Two issues:

1) mask shaders are ignored of drawImage; force application via a layer

2) visibility control clashes with layer controller; force a
   transparent shader for now

TBR=
Change-Id: Ic9a86c87db043745fa9f829ef36706525570a3be
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/299874
Reviewed-by: Florin Malita <fmalita@google.com>
Commit-Queue: Florin Malita <fmalita@google.com>
3 files changed