Support the beta markdown editor

[personalizedrefrigerator]

Summary

Adds support for the beta markdown editor.

Specifically, this pull request:

1. Updates the plugin build script to support importing CodeMirror 6 packages (the new build script is copied from the plugin template, see the editor plugin tutorial for details).
   • Upgrading the build script also required upgrading the dependencies in package.json to newer versions. The new versions were taken from the plugin template.
   • Types in api/ were not updated.
   • Because changes to package-lock.json are often difficult to review, changes to package-lock.json were not committed.
2. Splits the current index.js content script into two content scripts — one for CodeMirror 5 and one for CodeMirror 6.

Notes

• The CodeMirror 5 plugin seems to include additional logic for indenting lists. This logic was not included in the CodeMirror 6 plugin.
• This pull request also adds support for Joplin for Android — I've verified that this plugin 1) can be loaded in a custom build of Joplin 3.0.1 and 2) can be used to switch the "increase indent" button between adding spaces and adding tabs.

Testing

This pull request has been tested manually by:

1. Enabling the beta editor
2. Creating an opening <style> tag
3. Pressing enter
4. Verifying that the new line is indented with spaces
5. Changing the indentation setting from spaces to tabs in settings
6. Repeating steps 2-3 and verifying that the new line is indented with tabs.
7. Disabling "smart indent"
8. Creating an opening <style> tag and pressing enter
9. Verifying that the new line is not indented.
10. Indenting by pressing tab
11. Pressing enter and verifying that the new line is indented to match the previous.
12. Changing "how many spaces should a block be indented" to 8
13. Creating a list and indenting an item by pressing tab
14. Verifying that the new item is indented with 2 tabs
15. Disabling tab indentation
16. Repeating step 13 and verifying that indentation uses 8 spaces

Steps 2-11 were also tested in the legacy CodeMirror 5 editor.

Note: The above testing was done on Ubuntu 22.04 with Joplin 2.14.20. I have also verified that the modified version of the plugin can be used to enable space indentation in Joplin 2.11.11 with default settings.

[personalizedrefrigerator]

codeMirror5.ts is a version of indent.js, migrated to TypeScript and disabled in the CodeMirror 6 (beta markdown) editor.

[alondmnt]

Thanks a lot!