We also support interpolating from a CalculatedStyleValue to a
compatible dimension or percentage style value.
This also brings with it a couple of improvements in how we handle
interpolation between mixed dimension and percentage types in terms of:
- Proper simplification of the resulting calc()
- Improved handling of interpolation outside the 0-1 range
This removes the AnimationRefresh argument from `collect_animation_into`
which was added in a9b8840 - it's only effect was disallowing
`UseInitial`s within keyframes when we were doing animated style
updates which I believe is unintentional.
Gains us 214 WPT tests.
If a property is uses discrete interpolation and TransitionBehavior is
not set to `AllowDiscrete` that property should be non-transitionable.
This is now true for properties whose animation type is not discrete,
but the animation type falls back to discrete.
