fix(ngAnimate): use a fallback CSS property that doesn't break existing styles

The clip property seems to remove the box-shadow property when an absolute
positioned animation is ongoing. This fix changes the property to be border-spacing
which is also very underused. The border-spacing CSS property is only visible
when border-collapse is set to separate.

Closes #4902
Closes #5030
fix($animate): ensure keyframe animations are blocked around the reflow

Keyframe animations trigger on the first CSS class and not the second.
This may cause a slight flicker during a stagger animation since the
animation has already started before the stagger delay is considered.
This fix ensures that the animation is blocked until the active animation
starts which allows for staggering animations to take over properly.

Closes #5018