Multiple animation completions in a single update tracking issue

Currently, the AnimationPlayer doesn't handle animations correctly when a delta between 2 updates is greater than the duration of an AnimationClip. This issue tracks all the points that should be modified in order to handle correctly those cases:

- [ ] seek_time in ActiveAnimation::update

- [ ] animation events

- [ ] root motion

Start with AnimationPlayer and ActiveAnimation::update, then trace how animation events and root motion are processed during an update. The work is done when seek_time, animation events, and root motion all handle a delta between updates that exceeds an AnimationClip's duration.

Written by the indexing model from the issue text.