Escaping '#' inside bullet lists doesn't round-trip

[dionrhys]

Describe the bug
Within list items, # at the start of the text needs to be escaped to not turn the text into a heading. We can escape that by writing \#, but flipping between rich text and markdown removes the backslash, making the text within the list item a heading again.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://editor.stackoverflow.design/

2. Switch to Markdown mode and paste:

   \# test
   
   - \# test
   
   \# test

3. Flip to rich text mode, see that # is shown as expected

   Screenshot

   

4. Flip to Markdown mode, see that # is no longer escaped

   Screenshot

   

5. Flip to rich text mode, see that the text is now a <h1> heading

   Screenshot

   

Expected behavior
The editor should keep the needed backslash escape on the # character so that it doesn't turn the text into a heading.

Desktop (please complete the following information):

• OS: Windows
• Browser: Firefox
• Version: 107.0