SmoothTransition can not transition to/from a SimpleBlend

[Spitko]

First, a repro case, for your enjoyment: repro_heaps_SmoothBlend.zip

I've been trying to work with animations, and hit a rather troublesome bug/limit: Decompose not supported on transition. This prevents you from using SmoothTransition on SimpleBlend, which is a fairly sane thing to do when composing multi-layer animations.

Additionally, when calling playAnimation, this code always creates an instance. This is problematic for SmoothTransition, as this calls clone, which clones the child animations; but the children don't inherit their instance flag. As a result, playAnimation will always fail. I believe #955 is supposed to fix this, but the PR appears to be collecting dust.