In WYSIWYG mode, inputting # 1 does not render as a first-level heading

[baicie]

In WYSIWYG mode, inputting # 1 does not render as a first-level heading

A clear and concise description of what the bug is.

Try it here
https://nhn.github.io/tui.editor/latest/tutorial-example03-editor-with-wysiwyg-mode

To Reproduce

Steps to reproduce the behavior:

1. Creating a WYSIWYG editor
2. Enter # 1 and you will find that it does not become a first-level title.
3. Switch to markdown mode
4. You will find that how to get text value? how to convert MD to plain text or html text? #1 becomes how to get text value? how to convert MD to plain text or html text? #1

Expected behavior

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

Screenshots

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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context

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