The prior approach would consider all existing namespaces from back to front
to find the one that's the closest ancestor for a given host element. An
expensive `contains` operation was used which needed to traverse all the
way up the document root _for each existing namespace_. This commit implements
an optimization where the closest namespace is found by traversing up from
the host element, avoiding repeated DOM traversal.
Closes#45055
PR Close#45113
* The `TransitionAnimationEngine` had a fallback where it would store classes directly on a node if it doesn't have a `classList`. Presumably this is to support old browsers or if an animation is set on something like `ng-container`. This information was never used for anything since `containsClass` was never called. These changes simplify the logic to just a null check.
* Deprecates the `AnimationDriver.matchesElement` method, because it was only used in one place which can be replaced with `classList.contains`. We can't remove the method completely, because `AnimationDriver` is a public API. We also can't turn it into a method on the base class in order to remove it from the sub-classes, because it can break apps using `noImplicitOverride` while extending `AnimationDriver`.
PR Close#44378
JoostK