Support CodeMirror 6

[personalizedrefrigerator]

Summary

This pull request does two things:

1. Updates the plugin build script. This is required to require CodeMirror 6 packages.
   • The webpack.config.js file was updated to an unreleased version to support this. (See the relevant section in Joplin's beta markdown editor plugin tutorial).
2. Adds support for the CodeMirror 6-based beta markdown editor.

Notes

• This pull request does not commit generated updates to package-lock.json because such changes are difficult to review.
• Requires Joplin >= 2.14.16.
• This pull request is similar to Support CodeMirror 6 joplin-plugin-quick-links#15.

Testing

1. Enable the beta editor
2. Add an existing tag to a note using the plugin
   • Verify that text is preserved by default
3. Create a new tag using the plugin
   • Verify that text is still preserved
4. Disable "keep #tag text in the editor"
5. Add an existing tag to a note using the plugin
   • Verify that the completion text has been removed
6. Create a new tag using the plugin
   • Verify that the completion text has been removed
7. Create a code block
8. Try to link to a tag from the code block
   • Verify that the tag completion dialog doesn't appear.
9. Disable the beta editor and repeat steps 1-9.

This has been tested successfully on OpenSUSE Linux in Joplin 2.14.16 on commit 3286b5d.

untitled2.webm

[personalizedrefrigerator]

i and npm weren't in the original template and seem to be unused. As such, I have removed them here.

Please let me know if they should be added back.

[roman-r-m]

I can see in git log they were there from the very beginning, not sure why.

[roman-r-m]

Thank you for the PR.