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 agree with this, but honestly that is a separate issue --- the original strategy I had for this worked pretty well and respected the order of operations, but might be slightly more costly perf-wise (at least in v8) due to changing the shape of the class cache object. (see #9263)