fix($animate): ensure transition animations are unblocked before the dom operation occurs

Transitions are blocked when the base CSS class is added at the start of the animation. This
causes an issue if the followup CSS class contains animatable-styles. Now, once the animation
active state is triggered (when the animation CSS dom operation occurs) the animation itself
will always trigger an animate without a quick jump.

Closes #5014
Closes #4265
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