[ListItemOptions] Support line spacing for list items

[joeyliu7975]

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✅ I've searched other open/closed issues for duplicates before opening up this new issue.

Feature Request

We want list item to support line spacing, which will get developers room to create a more flexible and customized layout.

Describe alternatives you've considered

Since DownStylerConfiguration.paragraphStyle line spacing is modifiable, it may be inconvenient that if list item line spacing was immutable.