JupyterLab-MyST incompatible with HoloViz Panel

[riziles]

Describe the bug

No action required, just reporting an incompatibility issue:

Installing JupyterLab-MyST prevents Panel from correctly rendering Markdown components.

I love MyST, but I had to remove the JupyterLab extension because of this.

Reproduce the bug

1. Install Panel
2. Install JupyterLab-MyST
3. Add the following cell to a notebook:

import panel as pn
pn.extension()
pn.pane.Markdown("""
# What happened to all my headers????
""")

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[philippjfr]

I somewhat suspect this is caused by Panel adding a .markdown CSS class to the converted HTML tag. In Panel 1.x this should no longer be an issue because we render components into the shadow DOM which likely won't be affected by JupyterLab-MyST.

[rowanc1]

Thanks @riziles for the bug report and @philippjfr for the pointer!

If it is stealing the first header, it could also be that the markdown is being parsed by MyST with the frontmatter parsing being turned on (which tries to find the title, and then render as a title block in the first cell). There might be other compatibility issues as well, we will try to sort them out!