[Bug] Softline breaks and paragraphs aren't properly persed

### Bug Description

This basically continuation of this issue. https://github.com/AppFlowy-IO/appflowy-editor/issues/912
It seems editor still doesn't recognize softlines. Also after some update it actually converts paragraphs into the softline breaks during convert from MD format into the document

### How to Reproduce

1. use entry line like `First paragraph.\n\nSecond pargraph`
2. initialize editor using `markdownToDocument` function
3. convert editor document back to MD format using `documentToMarkdown` function

Output will be `First paragraph.\nSecond pargraph`, which 1 paragraph with softline break inside

### Expected Behavior

Output should be `First paragraph.\n\nSecond pargraph`

### Operating System

Any

### AppFlowy Editor Version(s)

v4, v5

### Screenshots

_No response_

### Additional Context

_No response_