Parse figcaption contents

### Check List

- [X] I have already read README.
- [X] I have already searched existing issues.
- [X] I have already searched existing pull requrests.

### Feature Request

When using the `figcaption` option,

```
marked:
figcaption: true
```
generating images as
```

...

```
the figcaptions are usually intended to be rendered in some fancy way, including links or styles, etc.

I think it would be useful to parse its contents, changing from:
```
return `${out}${text}`;
```
to
```
return `${out}${marked.parse(text)}`;
```

If the figcaption has no special markdown, there is no difference. If we include some kind of markdown content, it will be parsed.

### Additional context

_No response_