Mobile Rich Text Editor: Render more content in the editor

[personalizedrefrigerator]

The mobile Rich Text Editor should be updated to support rendering and editing the following Markdown:

• ==highlight==s — Mobile: Rich Text Editor: Support rendering subscript, superscript, and highlighted formatting #12944
• [toc]s — Mobile: Rich Text Editor: Support rendering table of contents blocks #12949
  • The Markdown [toc] generates a table of contents. Currently, editing a note that contains a [toc] expands the [toc] into a list of links.
• <sub> and <sup> — Mobile: Rich Text Editor: Support rendering subscript, superscript, and highlighted formatting #12944
• <details> — Mobile: Rich Text Editor: Add basic support for collapsible <details> blocks #12946
• Footnotes
  • The ProseMirror footnotes tutorial might be helpful when implementing this.

[personalizedrefrigerator]

Correctly rendering [toc]s and footnotes seems to be more difficult than I expected. For now, I plan to focus on adding support for <sup>/<sub>/==highlight==.