Log the time until the Animation finishes as "Animating" (#34538)

Stacked on #34522.

<img width="1025" height="200" alt="Screenshot 2025-09-19 at 6 37 28 PM"
src="https://github.com/user-attachments/assets/f25900f6-6503-48b1-876d-bd6697a29c6f"
/>

We already cover the time between "Starting Animation" and "Remaining
Effects" as "Animating". However, if the effects are forced then we can
still be animating after that. This fills in that gap.

This also fills in the gap if another render starts before the animation
finishes on the same track. It'll mark the blank space between the
previous render finishing and the next render starting as "Animating".

This should correspond roughly to the native "Animations" track.