show indentation in code editor

[typemytype]

from @djrrb:

In teaching classes/workshops, I have found that indentation tends to be a challenge for folks who are new to Python. Since the Drawbot editor is intended to help beginners, I think an editor preference to show tabs might be very helpful...if it’s not too difficult to add!

There are a few ways to visualize this: greyed-out middots for each space, vertical lines, etc.

Talking to @robstenson about this topic, he suggested the Indent Rainbow VSCode extension, which clearly but subtly color codes tabs to help students easily identify the indentation level of a code block. (He also showed me Rainbow Brackets as well, which is pretty cool.)

If this should be a github issue, let me know, but I figured I would start here because I prefer typing my feature requests in DBRegular! 😎

Thank you!

see https://forum.drawbot.com/topic/286/show-tabs-in-editor

todo:

Create a custom NSLayoutManager for the code editor and overwrite drawGlyphsForGlyphRange_atPoint_ and draw something like a rainbow or dots or ...

also see https://github.com/coteditor/CotEditor/blob/89afb53f207309bfee2b1070ada3f258e1e0d6ef/CotEditor/Sources/LayoutManager.swift#L312