[Feature request] Spell check

[batchor]

Context

• [x] This issue is not a bug report. (please use a different template for reporting a bug)
• [ ] This issue is not a duplicate of an existing issue. (please use the search to find existing issues)

Description

This feature request is duplicated with #1977 for spell check

Spell check by 3rd-party tools such as the browser or other tools like Grammarly is useful when writing documents and Markdown. I think this is not a heavy work for core developers but it brings huge benefit to users. All we need is to add contenteditable="true" attribute to each editor element.

The CodeMirror editor supports spell check by default.

Please consider this feature request. Anyone who expects this feature to be implemented, please upvote!