[skotty] Native SkPath interpolation

SkPath supports interpolation, no reason to handle that explicitly in
Skotty.

Change skotty::ShapeValue to convert to SkPaths upfront, when parsing,
and then rely in native interpolation.

TBR=
Change-Id: I32d424ea359e0736909d4e51602ffeb14403feed
Reviewed-on: https://skia-review.googlesource.com/90362
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
3 files changed