[Feature]: Highlight current paragraph in preview pane

[Ethkuil]

Feature Description
Highlight current paragraph in preview pane. Just like this:

Background
This feature will make it much easier to find corresponding elements in preview pane, especially when there are some complex elements.

Proposed Solution (Optional)
I found this feature useful in https://ui.toast.com/tui-editor. It's a open-source Markdown editor. So I think it a good idea to simply refer to its implementation of nhn/tui.editor.

Priority (Optional)

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