fix(ngAnimate): defer DOM operations for changing classes to postDigest

When ngAnimate is used, it will defer changes to classes until postDigest.
Previously, AngularJS (when ngAnimate is not loaded) would always immediately
perform these DOM operations.

Now, even when the ngAnimate module is not used, if $rootScope is in the midst
of a digest, class manipulation is deferred. This helps reduce jank in
browsers such as IE11.

/CC @tbosch --- alternative/more general fix here

Closes #8234
Closes #9263
I understand matsko is working on the ordering fix, so with all those comments addressed does it LGTY? it would be good to merge it so that it's easier for matias to consistently fix `resolveElementClasses()` in core and ngAnimate