[skottie] One-node camera support

So far Skottie has been assuming all cameras are two-node (have a point
of interest).

AE also supports one-node cameras, where the camera does not auto-orient
towards a POI but starts off perpendicular to the z == 0 plane.

(https://helpx.adobe.com/after-effects/how-to/camera-animation.html)

Change-Id: Id565de7d8feb9a762940ac372c1bbbcce2e2dfc6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/254559
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
4 files changed