VideoPress: Chapters parsing from description field not working in P2 editor

### Impacted plugin

None / Other

### Steps to Reproduce

1. Using video or videopress block, add a video in a P2 post
2. Edit the `Description` field and add some timestamps and a label for chapters:
```
00:00 Intro
00:10 Chapter 1
```
3. Save the post and view it on P2.
4. Observe the the chapters are not applying to the video.

### A clear and concise description of what you expected to happen.

Chapters should be parsed and saved when added to a video in the P2 editor.

### What actually happened

No chapters are displayed.

### Browser

Google Chrome/Chromium, Mozilla Firefox, Microsoft Edge, Apple Safari, iOS Safari, Android Chrome

### Other information

_No response_

### Platform (Simple, Atomic, or both?)

Simple, Atomic, Self-hosted

### Reproducibility

Consistent

### Severity

Some (< 50%)

### Available workarounds?

No but the platform is still usable

### Workaround details

If you edit the post in the wp-admin block editor, the chapters will save fine.

Reproduce the issue with the VideoPress block's Description field in the P2 editor, using the timestamp example, and compare it with the wp-admin block editor where chapters save correctly. Trace the VideoPress block and P2 editor handling until the description reaches chapter parsing; done means the same chapters are saved and displayed on P2.

Written by the indexing model from the issue text.