animation: fix infinitely growing models list

https://crrev.com/c/4605129 made it so that an updated animation in
Blink resulting in a cancel/re-create of a compositor animation would
reuse the compositor animation's id and group, causing it to push new
properties to the existing compositor-thread animation, rather than
creating a new animation. While this preserves the Animation and
KeyframeEffect, it pushes new KeyframeModels - removing the old ones.

However, grouped KeyframeModels will not be deleted until every model in
the group is finished. Since the incoming KeyframeModels have the same
group as the to-be-removed models, this doesn't happen until the new
models complete. However, some animations may never complete, leading to
unbounded growth.

This CL fixes the issue by setting the replaced group_id on a
KeyframeEffect performing this replacement. When the incoming keyframe
models are activated, the completed ones, matching the KeyframeEffect's
replaced group_id, have their group id removed. This allows them to be
deleted immediately and also prevents the model from dispatching a
finished event, since it's conceptually been "updated" rather than
deleted.

[1] https://source.chromium.org/chromium/chromium/src/+/main:cc/animation/keyframe_effect.cc;l=1024;drc=07bd1fe6394d0575e95b8211c872d851784f1d66

Change-Id: I5783b92285997a3a90cbb6563412f768f8978774
Bug: 323708859
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5300130
Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: David Bokan <bokan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1264266}