Log Custom Reason for the Suspended Commit Track (#34522)

Stacked on #34511.

We currently log all Suspended Commit as "Suspended on Images or CSS"
but it can really be other reasons too now. Like waiting on the previous
View Transition. This allows the host config configure this reason.

Now when one animation starts before another one finishes we log that as
"Waiting for the previous Animation".

<img width="592" height="257" alt="Screenshot 2025-09-17 at 11 53 45 PM"
src="https://github.com/user-attachments/assets/817af8b5-37ae-46d8-bfd1-cd3fc637f3f3"
/>