As a follow-up, we could move all the data living under a mutex in the
SharedLayoutContext only in order to create the local context to the same place.
This should increase animation performance when there are multiple animations in
one page that happen to be on different threads.
There's a bit of flickering when unpausing where the node has the original
state, but I'm not totally sure where it comes from, posibly from
PropertyAnimation returning None due to no styles changing?
There's some maths I've done wrong, but it DOES animate some things, though
they're only triggered past the first restyle, and we probably have some
duplications where the animations arrive to layout.
Anyway, got to go.
