Support the CodeMirror 6 beta editor

[personalizedrefrigerator]

Summary

Adds more complete support for the CodeMirror 6 beta editor.

Important

Requires this upstream pull request to be merged.

Screen recording

untitled.mp4

Notes

• The plugin's list indentation functionality still doesn't work.
• With Desktop: Improve beta editor support for the Rich Markdown plugin laurent22/joplin#9935, the CodeMirror 6 editor has both cm-editor and CodeMirror classes. The CodeMirror 5 editor has only CodeMirror.
• tok-meta seems to include bold, italic, and header markings.
• CodeMirror 6 has only one wrapper element per line. As such, CodeMirror-activeline-background and CodeMirror-activeline apply to the same element.
• Locally, I had to update the Joplin plugin template to build the plugin. These changes were not committed.

[CalebJohn]

Thanks for this! I've been looking forward to your CodeMirror 6 work for awhile.

What's the upgrade plan on the Joplin side? Eventually I would like to drop Codemirror 5 compat and bump the min version of this plugin. Is the current plan to have both exist side-by-side for awhile?

[personalizedrefrigerator]

What's the upgrade plan on the Joplin side? Eventually I would like to drop Codemirror 5 compat and bump the min version of this plugin. Is the current plan to have both exist side-by-side for awhile?

If everything goes well, the CodeMirror 6 editor will be the default editor for Joplin version 3.0. The current plan is to keep the CodeMirror 5 editor for a few versions as an opt-in through settings. The compatibility layer will likely be kept for longer, but not indefinitely.

[CalebJohn]

Thanks @personalizedrefrigerator! This looks good. I'll hold off gutting Codemirror 5 support for now.